retired, specially assigned under RSA 490:3. The State appeals the Superior Court’s (Brown, J.) ruling that RSA chapter 100-C (Supp. 2011), the Judicial Retirement Plan, violates Part I, Article 23 of the New Hampshire Constitution. The petitioner and intervenors cross-appeal the court’s ruling that salary raises provided for by Laws 2003, 311:3 and Laws 2005,177:96 should not be included in calculating benefits under the prior retirement statutes. We affirm in part, reverse in part, and remand.
The petitioner, Raymond A. Cloutier, is a retired probate court judge. The six intervenors are retired supreme, superior, probate, and district court judges. We refer to them collectively as the petitioners. In October *4482008, Cloutier submitted a written request to the Board of Trustees of the New Hampshire Judicial Retirement Plan (board) asserting that his retirement allowance was erroneously calculated pursuant to RSA chapter 100-C, and that he was entitled to benefits under the retirement statutes that were in effect when he was appointed to be a judge. The board denied his claim and Cloutier filed a petition for writ of certiorari in the superior court. The parties subsequently filed cross-motions for summary judgment.
In response to the trial court’s order, the parties filed a joint stipulation containing a chart with projected lifetime retirement payouts for Cloutier. The projected payouts included several separate calculations, comparing retirement benefits under the plan enacted pursuant to RSA chapter 100-C and the previous retirement statutes repealed by Laws 2003, 311:10. The parties disputed certain assumptions underlying the calculations, but not the mathematical calculations within the projections. As the stipulation provides,
The Parties stipulate that only the mathematical calculations ... are fair and accurate, and fully reserve the right to challenge the propriety of the following assumptions as a matter of law, so that the court may find that there are no genuine issues of material fact in dispute and rule on the following questions of law . . . :
a. Whether the 10% raise given by Laws 2003, 311:3 should be included in calculating and projecting retirement benefits under the old plan;
b. Whether the 1.01% raise given by Laws 2005,177:96 should be included in calculating and projecting retirement benefits under the old plan;
c. Whether future legislative salary increases are more appropriately determined by the average of salary increases given to sitting probate judges in the period since the new plan’s inception (from January 1, 2005 forward), or, alternatively, the average [of] all legislative salary increases given to sitting probate court judges from 1991 to present;
d. Whether Laws 2003, chapter 311 and subsequent amendments to RSA chapter 100-C constitute a “substantial impairment” of Petitioner’s and Intervenors’ retirement benefits within the meaning of Part I, Article 23 of the State Constitution.
Following a hearing, the trial court granted summary judgment for the petitioners, concluding that the application of RSA chapter 100-C to judges *449who accepted their positions before its enactment results in impairment of contract rights in violation of the New Hampshire Constitution. The trial court, however, rejected the petitioners’ assertion that the ten percent and one percent salary increases authorized in 2003 and 2005 should be included in calculating their benefits under the prior retirement statutes. This appeal followed.
The State raises two issues on appeal: (1) whether the trial court erred in ruling that RSA chapter 100-C violates Part I, Article 23 of the New Hampshire Constitution; and (2) in the event the trial court’s ruling is upheld, whether RSA chapter 100-C is unconstitutional only as applied to judges who met the service and age requirements for retirement as of January 1, 2005. The petitioners cross-appeal, arguing that the trial court erred in ruling that the 2003 and 2005 salary raises are not properly included as “currently effective annual salary” when calculating their retirement benefits.
Prior to the enactment of RSA chapter 100-C, a series of statutes provided for retirement benefits to judges who retired after meeting specific service and age requirements. See RSA 490:2 (1977) (repealed 2003) (supreme court); RSA 491:2 (1977) (repealed 2003) (superior court); RSA 502-A:6-a (1977) (repealed 2003) (district court); RSA 547:2-a (1997) (amended 2003) (“Full-time probate judges ... shall be entitled to the same disability and retirement benefits as fullrtime justices of the district court”). When the petitioners were appointed to be judges, the prior retirement statutes were in effect.
Under the prior retirement statutes, as “additional compensation for services rendered and to be rendered,” a judge who retired upon attaining the age of seventy years having served as a judge for at least seven years, or upon attaining the age of sixty-five years having served for at least ten years, was entitled to receive for the rest of his or her life an annual amount equal to seventy-five percent of “the currently effective annual salary of the office” from which the judge was retired. RSA 502-A:6-a, III (repealed 2003); RSA 490:2, II (repealed 2003); RSA 491:2, II (repealed 2003). The statutes provided that a “sum sufficient to pay any and all benefits or compensation... is hereby continually appropriated therefor” and that the “governor is authorized to draw his warrant for the payment thereof out of any funds in the treasury not otherwise appropriated.” RSA 490:2, VI (repealed 2003); RSA 491:2, VI (repealed 2003); RSA 502-A:6-a, VI (repealed 2003).
In 2003, the prior retirement statutes were repealed and replaced with RSA chapter 100-C. See Laws 2003, ch. 311. Implementation of the new statute was delayed until the Internal Revenue Service made a favorable determination as to the tax qualified status of the plan. See Laws 2003, *450311:11. The parties have stipulated that RSA chapter 100-C took effect on January 1, 2005. Between 2006 and 2009, the petitioners retired from full-time service.
Under the new retirement statute, membership in the judicial retirement plan is mandatory for any full-time supreme, superior, district or probate court judge. RSA 100-C:3. Retirement benefits are established as follows:
I. Any member who has at least 15 years of creditable service and is at least 60 years of age, or who has at least 10 years of creditable service and is at least 65 years of age, or who has at least 7 years of service and is 70 years of age may retire on a service retirement allowance ....
II. A member who is at least 65 years of age with 10 years of creditable service may retire on a service retirement allowance equal to 75 percent of the member’s final year’s salary.
III. A member who is 70 years of age with 7 years of creditable service may retire on a service retirement allowance equal to 45 percent of the member’s final year’s salary. A member who is 70 years of age shall be granted an additional 10 percent over the 45 percent level for each year of creditable service the member has over 7 years.
TV. A member who is at least 60 years of age with at least 15 years of service may retire on a service retirement allowance equal to 70 percent of the member’s final year’s salary. A member who has at least 15 years of service and is at least 60 years of age shall be granted an additional percent over the 70 percent level for each year of continued service over 15 years.
V. Under no circumstance shall any service retirement allowance pursuant to this section exceed 75 percent of the member’s final year’s salary.
VI. Any member attaining eligibility for 75 percent of the member’s final year’s salary shall not be required to make employee contributions to the plan pursuant to RSA 100-C:14.
RSA 100-C:5, I-VI.
The new retirement plan is self-funding, relying upon contributions from the State and the judges. See RSA 100-C:13. Although the new retirement statute limits benefits to seventy-five percent of the judge’s final year’s *451salary, the board has the discretion to award cost-of-living adjustments to retired judges up to an aggregate amount of $50,000 per year, and to award more than that amount with the approval of the legislature. RSA 100-C:13, 111(g); RSA 100-C:17. The legislature may approve cost-of-living adjustments in excess of $50,000 only if the plan’s annuity fund earns at a level greater than the actuarial assumed rate of return approved by the board and the trust is at least ninety percent funded for the calendar year. RSA 100-C:17.
The State argues that the trial court erred in finding a violation of Part I, Article 23 of the State Constitution because the prior retirement statutes did not create contractual rights and, even if they did, those rights have not been substantially altered by RSA chapter 100-C. Because the parties rely only upon the State Constitution, we need not engage in a separate federal analysis. See Petition of Guardarramos-Cepeda, 154 N.H. 7, 9 (2006).
In reviewing the trial court’s grant of summary judgment, we consider the affidavits and other evidence, and all inferences properly drawn from them, in the light most favorable to the non-moving party. If our review of that evidence discloses no genuine issue of material fact, and if the moving party is entitled to judgment as a matter of law, we will affirm the grant of summary judgment. We review the trial court’s application of the law to the facts de novo.
State v. N. of the Border Tobacco, 162 N.H. 206, 212 (2011) (citations omitted).
Whether or not a statute is constitutional is a question of law, which we review de novo. Tuttle v. N.H. Med. Malpractice Joint Underwriting Assoc., 159 N.H. 627, 640 (2010).
The party challenging a statute’s constitutionality bears the burden of proof. The constitutionality of an act passed by the coordinate branch of the government is presumed. It will not be declared to be invalid except upon inescapable grounds; and the operation under it of another department of the state government will not be interfered with until the matter has received full and deliberate consideration.
Id. (quotations, citations and brackets omitted).
Part I, Article 23 of the New Hampshire Constitution provides: “Retrospective laws are highly injurious, oppressive, and unjust. No such *452laws, therefore, should be made, either for the decision of civil causes, or the punishment of offenses.” Although this provision does not specifically reference existing contracts, “we have held that its proscription duplicates the protections found in the contract clause of the United States Constitution.” State v. Fournier, 158 N.H. 214, 221 (2009) (quotation omitted). “We therefore understand article I, section 10 [of the Federal Constitution] and part I, article 23 [of the State Constitution] to offer equivalent protections where a law impairs a contract, or where a law abrogates an earlier statute that is itself a contract.” Opinion of the Justices (Furlough), 135 N.H. 625, 630 (1992). Accordingly, “every statute which takes away or impairs vested rights, acquired under existing laws,... must be deemed retrospective” within the meaning of Part I, Article 23. Tuttle, 159 N.H. at 641 (quotation omitted).
Contract Clause analysis in New Hampshire requires a threshold inquiry as to whether the legislation operates as a substantial impairment of a contractual relationship. This inquiry has three components: whether there is a contractual relationship, whether a change in law impairs that contractual relationship, and whether the impairment is substantial. If the legislation substantially impairs the contract, a balancing of the police power and the rights protected by the contract clause[] must be performed, and the law may pass constitutional muster only if it is reasonable and necessary to serve an important public purpose.
Id. (quotations, citations, ellipses and brackets omitted).
Whether a public retirement plan creates a contract between a public employee and the State is a question of first impression in New Hampshire. “The nature of pension rights of a public employee is a question which has caused courts great difficulty.” Wagoner v. Gainer, 279 S.E.2d 636, 640 (W. Va. 1981). “Development of the law on the question has been long and tort[u]ous, reflecting the increasing pressure placed upon the judiciary by the evolution of the now generally accepted theory that pensions are a part of the compensation of an employee to which, under ordinary circumstances, he is as much entitled as he is to the wages paid him for the work he has actually performed.” Id. (quotation and ellipses omitted).
Regarding public employees, we have recognized that
[a]n employee’s compensation is not necessarily limited to his salary, but will include any other benefits that are an integral part of the employee’s contemplated compensation. These benefits may include... retirement... benefits. Such benefits are a means by which the State can attract qualified persons to enter and *453remain in State employment, and an employee accepts an offer of employment or continues in employment with the State in reliance on the State’s representations that it will provide such benefits. These benefits are an integral part of the contemplated compensation and become vested at the time one becomes a permanent State employee or continues in such employment.
Jeannont v. N.H. Personnel Comm’n, 118 N.H. 597, 601-02 (1978). We have also held that RSA chapter 100-A, establishing the New Hampshire Retirement System, “clearly entitles certain governmental employees to receive retirement and other related benefits.” State Employees’ Ass’n of N.H. v. Belknap County, 122 N.H. 614, 621 (1982). “These benefits constitute a substantial part of an employee’s compensation and become vested upon the commencement of permanent employee status. Designed to attract competent individuals into government service, the benefits are essentially created for the protection of the employee and his family.” Id. (citations omitted); see also Gilman v. County of Cheshire, 126 N.H. 445, 448-49 (1985) (right to receive sick leave benefits vests when one becomes a governmental employee or continues in such employment). One of the primary purposes of providing benefits to public employees is “to induce competent persons to enter and remain in public employment. Benefits would serve as little inducement if they could be whisked away at the whim of the public employer.” Gilman, 126 N.H. at 449.
In support of the statement in Jeannont that “benefits are an integral part of the contemplated compensation and become vested at the time one becomes a permanent State employee or continues in such employment,” Jeannont, 118 N.H. at 602, we cited Kern v. City of Long Beach, 179 P.2d 799 (Cal. 1947), and Bakenhus v. City of Seattle, 296 P.2d 536 (Wash. 1956). In Kern, the Supreme Court of California reasoned that “public employment gives rise to certain obligations which are protected by the contract clause of the Constitution, including the right to the payment of salary which has been earned. Since a pension right is an integral portion of contemplated compensation, it cannot be destroyed, once it has vested, without impairing a contractual obligation.” Kern, 179 P.2d at 802 (quotation and citation omitted). In Bakenhus, the Supreme Court of Washington rejected as “insupportable” the view that since the right to receive a pension does not arise until all the conditions are fulfilled, the employee’s rights must depend upon the law as it exists at that time. Bakenhus, 296 P.2d at 539. Rather, the court adopted the “more enlightened” view that “the employee who accepts a job to which a pension plan is applicable contracts for a substantial pension and is entitled to receive the same when he has fulfilled the prescribed conditions.” Id. at 540.
*454Other state supreme courts that have been presented with this issue have held that a judge’s pension rights are an integral element of compensation and a vested contractual right accruing upon acceptance of employment. See, e.g., Board of Tr. of Pub. Emp. Ret. F. v. Hill, 472 N.E.2d 204, 208-09 (Ind. 1985); Gainer, 279 S.E.2d at 643; Olson v. Cory, 636 P.2d 532, 535-36 (Cal. 1980); Miles v. Tenn. Consol. Retirement System, 548 S.W.2d 299, 304 (Tenn. 1976); Sylvestre v. State, 214 N.W.2d 658, 664-65 (Minn. 1973); Campbell v. Michigan Judges Retirement Board, 143 N.W.2d 755, 757-58 (Mich. 1966). As the Minnesota Supreme Court explained:
[A] judge gives up the right to continue in the only field of endeavor in which he has been educated and is experienced in order to accept a position, often for a much smaller financial reward, anticipating that upon retirement the state will continue to pay him part of his salary. Inflation affects retired judges the same as it does anyone else; and a judge’s reliance upon the state’s offer to pay, upon his retirement, a part of the salary allotted to his office surely is one of the significant considerations that induces the judge to remain in office during the required period of time and until the age permitting retirement. Frequently, his retirement compensation is the only resource he has to rely upon when he has reached an age where it is too late to actively engage in any other financial activity.
Sylvestre, 214 N.W.2d at 666.
In the case before us, the prior retirement statutes stated unequivocally that judicial retirement pay was “additional compensation for services rendered and to be rendered.” RSA 490:2 (repealed 2003); RSA 491:2 (repealed 2003); RSA 502-A:6-a (repealed 2003). For the reasons set forth above, we agree with the weight of authority that these statutes created an implied-in-fact contract between the State and the judges who entered into employment when the statutes were in effect, which vested when they were appointed to be judges subject to attaining the age and service requirements. Because we hold that there is a contractual relationship between the State and the petitioners, we address whether RSA chapter 100-C impairs that contractual relationship and, if so, whether the impairment is substantial.
The trial court found that because the prior retirement statutes allowed for the calculation of retirement benefits based upon the most recent adjustments in judicial salaries, and because the new statute bases benefits on the amount the judge was being paid at the time of retirement, the new statute “is clearly an impairment of the plaintiffs’ vested rights *455under the previous statutory benefit.” We agree with the trial court that RSA chapter 100-C impairs the obligations entered into under the prior retirement statutes. The petitioners had the right to expect that upon retirement their pension would reflect subsequent increases in pay granted to those in active service.
The trial court also found that the impairment is substantial. In doing so, the court relied upon Tuttle and Opinion of the Justices (Furlough). We disagree that these cases compel the conclusion reached by the trial court. The court quoted language in Tuttle which states that “ ‘[w]here the right abridged was one that induced the parties to contract in the first place, a court can assume the impairment to be substantial.’ ” Tuttle, 159 N.H. at 649 (quoting Fraternal Order of Police Lodge No. 89 v. Prince George’s County, Md., 645 F. Supp. 2d 492, 510 (D. Md. 2009)). We hesitate, however, to adopt this language as the basis for finding substantial impairment in this case. Because the parties’ reliance was not at issue in Tuttle, the quoted language is dicta. See Tuttle, 159 N.H. at 650. In addition, the opinion from which the Tuttle court quoted was subsequently reversed. See Fraternal Order of Police Lodge No. 89 v. Prince George’s County, Md., 608 F.3d 183 (4th Cir. 2010).
The trial court also relied upon Opinion of the Justices (Furlough), 135 N.H. at 634, and, quoting Furlough, concluded that because the impairment affects the “very heart of an employment contract: the promise of certain work for certain income,” RSA chapter 100-C is a substantial impairment of the contract between the petitioners and the State. In Opinion of the Justices (Furlough), the terms of a collective bargaining agreement between the State and certain public employees established the basic workweek as thirty-seven and one-half hours per week. Furlough, 135 N.H. at 631. Proposed legislation would have required employees to take a certain number of unpaid days of leave. Id. at 628. In concluding that the legislation would constitute a substantial impairment of the contract between the State and the employees, we noted that “[t]he affected employees have surely relied on full paycheeks to pay for such essentials as food and housing. Many have undoubtedly committed themselves to personal long-term obligations such as mortgages, credit cards, car payments, and the like.” Id. at 634 (quotation omitted). It was in this context that we concluded: “The bill under consideration here impairs the very heart of an employment contract: the promise of certain work for certain income. Its impact would likely wreak havoc on the finances of many of the affected workers and can only be considered substantial.” Id. In contrast, unlike an employment contract that guarantees definite hours of work for a definite amount of compensation, there is no absolute certainty from year to year whether any upward modifications to judicial salaries will be *456legislatively authorized. In fact, the parties have stipulated that in eight of the years between 1991 and 2010, there was no increase in judicial salaries.
In determining the issue of substantial impairment, we look again to the cases favorably cited in Jecmnont. In Kern, the court addressed the issue of modifications by the government in a pension system prior to the time for commencement of payments and concluded that “an employee may acquire a vested contractual right to a pension but . . . this right is not rigidly fixed by the specific terms of the legislation in effect during any particular period in which he serves.” Kern, 179 P.2d at 803. The court reasoned that “[t]he statutory language is subject to the implied qualification that the governing body may make modifications and changes in the system. The employee does not have a right to any fixed or definite benefits, but only to a substantial or reasonable pension.” Id. Therefore, the court found no inconsistency in holding that the employee “has a vested right to a pension but that the amount, terms and conditions of the benefits may be altered.” Id.; see also Betts v. Bd. of Admin. of Pub. Emp. Ret. System, 582 P.2d 614, 617 (Cal. 1978) (alterations of employees’ pension rights must bear some material relation to the theory of a pension system and its successful operation, and changes in a pension plan which result in disadvantage to the employees should be accompanied by comparable new advantages).
In Bakenhus, the court held that “the employee who accepts a job to which a pension plan is applicable contracts for a substantial pension and is entitled to receive the same when he has fulfilled the prescribed conditions.” Bakenhus, 296 P.2d at 540. The court reasoned that the employee’s pension rights “may be modified prior to retirement, but only for the purpose of keeping the pension system flexible and maintaining its integrity.” Id. According to the court, “[t]his view, while it may not be flawless in a purely legalistic sense, gives effect to the reasonable expectations of the employee and at the same time allows the legislature the freedom necessary to improve the pension system and adapt it to changing economic conditions.” Id.
Several other jurisdictions approve the view that, prior to retirement, a plan may be changed only if there is a corresponding change of a beneficial nature to the employee. See, e.g., Police Pension and Relief Board of Denver v. Bills, 366 P.2d 581, 584 (Colo. 1961) (prior to eligibility to retire, there is limited vesting of pension rights such that although the plan could be changed, it could not be abolished nor could there be a substantial change of an adverse nature without a corresponding change of a beneficial nature); In re Marriage of Alarcon, 196 Cal. Rptr. 887, 892 (Ct. *457App. 1983) (while vested rights to pension benefits may be modified before a retirement to keep a pension system flexible and permit adjustments to accord with changing conditions, such modifications must be reasonable and not destroy or impair a vested contractual right to a pension); Gainer, 279 S.E.2d at 644 (changes in the pension plan may be allowed if any disadvantages are counter-balanced by advantages, i.e., substitute consideration); Sylvestre, 214 N.W.2d at 666 (taking away the right to receive compensation without any compensating benefits constitutes an impairment of contract). Because we reject the approach adopted by the trial court, we reverse and remand this issue for the court to determine in the first instance whether the contractual impairment is offset by any compensating benefits under RSA chapter 100-C.
The petitioners argue in their cross-appeal that the trial court incorrectly excluded the ten percent and one percent salary increases authorized in 2003 and 2005 in calculating their benefits under the prior retirement statutes. Laws 2003, 311:3 amended RSA 491-A:1 to increase the salary of each judicial position by ten percent. This increase became effective on January 1, 2005, the effective date of RSA chapter 100-C. The ten percent increase matched the contribution of ten percent of earnable compensation that judges are required to make to the new plan. See RSA 100-C:14. This salary increase was expressly intended not to apply to judges who had already retired and were receiving benefits under the prior retirement statutes. See Laws 2003,311:6. Because the judges’ contribution to the new plan was also based upon the ten percent increase, in 2005 judicial salaries were increased by one percent to correct for that effect. See Laws 2005, 177:96. The board determined that because the 2005 pay raise was a technical correction of the 2003 raise, it also had to exclude the one percent increase from the calculation of retirement benefits under the prior retirement statutes.
The petitioners argue that these increases should be included in the base calculation of retirement benefits payable under the prior statutes because: (1) the prior retirement statutes calculate benefits as seventy-five percent of the “currently effective salary” for sitting judges; (2) Laws 2003, chapter 311 did not purport to exclude the salary increase from the calculation of the petitioners’ benefits payable under the prior plan; and (3) excluding the ten percent raise violates Part I, Article 23 of the State Constitution. The board argues that chapter 311 “clearly and unambiguously” provides that the ten percent increase is not included in determining retirement benefits pursuant to the prior retirement statutes and that the salary increase was a one-time adjustment to judicial salaries equal to contributions required by the new plan. The board further argues that the ten percent increase was not “salary” under the prior retirement statutes because its only *458purpose was to compensate for the ten percent employee contribution the judges had to make upon the effective date of the new plan.
We are persuaded by the board’s position that these salary adjustments were authorized for the limited purpose of compensating judges for their ten percent earnable compensation contribution required under the new retirement plan. Therefore, these adjustments may not be characterized as “effective annual salary” for purposes of calculating benefits under the prior retirement statutes. Accordingly, we affirm the trial court on this issue.
Affirmed in part; reversed in part; and remanded.
Fitzgerald, J., retired superior court justice, and Carroll, J., circuit court justice, specially assigned under RSA 490:3, concurred; Manias and Bean, JJ., retired superior court justices, specially assigned under RSA 490:3, concurred in part and dissented in part.