After the decision in Ryder v. Brockton Savings Bank, 238 Mass. 52, Mary L. Ryder, in accordance with the terms of the decree affirmed in that case, on May 25, 1921 re*63deemed three mortgages given by her husband, Henry H. Ryder, to that bank. She thereupon held title to said notes and mortgages “as if she were an assignee in due course with all the rights of enforcement and transfer and all other rights that the original holder” had. Immediately after redemption, Mrs. Ryder assigned the mortgages to John J. Sullivan who now owns them.
In the present suit Merton F. Ellis, who is the owner of the equity of redemption in the premises described in said mortgages, seeks an accounting and a decree entitling him to redeem. John J. Sullivan, hereinafter called the defendant, and Mary L. Ryder were named as defendants, but the bill has been dismissed as to Mrs. Ryder and no question is made as to the propriety of that action. The final decree authorized redemption as against Sullivan and the case is here upon the appeal of Ellis who complains that there is error in the computation of the amounts to be paid and in the determination of the rights secured to him upon redemption.
The plaintiff contends that there was error because in order to redeem he must pay interest at the rate of six per cent per annum upon the principal sum secured by the mortgages, instead of the lower rates written in the notes and mortgages. On March 1, 1918, the plaintiff was the owner of the equity of redemption in the premises described in these mortgages and on that date it is conceded that the interest was “increased by agreement of parties ” to six per cent per annum. On the record it must be assumed that this agreement was made by the plaintiff and the Brockton Savings Bank, and that it was definite and valid. The plaintiff was not entitled to redeem, except upon compliance therewith. The agreement related to the mortgages, the rate of interest being incidental thereto, and the defendant is entitled to its benefit. A court of equity will not aid one who owns property subject to a mortgage to redeem, except upon compliance with his binding agreement upon which the mortgage thereafter has been held as security for an amount different from that for which it originally was written. Joslyn v. Wyman, 5 Allen, 62. Whitney v. Metallic Window Screen Manuf. Co. 187 Mass. 557, 560. The plaintiff, if he desires to redeem, must pay the interest required by his agreement and which, it may be noted, was in fact paid by Mrs. Ryder to the savings bank.
*64The defendant on May 26, 1921, notified the plaintiff that thereafter interest would be charged on said mortgages at the rate of seven and one half per cent per annum, but the plaintiff refused to pay the increase. His refusal was justified. The amounts payable could not be increased except by agreement of the parties standing in the position of mortgagor and mortgagee. From an analysis of the amount fixed by the decree, it appears that it provided for the payment of interest at seven and one half per cent per annum, from May 25, 1921 to July 1, 1921. Undoubtedly this was by inadvertence, as the interest payable after July 1,1921, was fixed at six per cent. The decree must be modified accordingly.
Under the decree the plaintiff, in order to redeem, must pay interest not only on the principal sums secured by the mortgages, but after May 25, 1921, simple interest on the overdue interest paid to the Brockton Savings Bank. It has long been settled that interest on interest cannot be recovered, although payment has been demanded, because of “the ancient unwillingness to allow compound interest.” Lewin v. Folsom, 171 Mass. 188, 192. Tisbury v. Vineyard Haven Water Co. 193 Mass. 196. While this is the general rule, it is not always followed. In equity interest may be compounded and in the discretion of the court may be allowed where it is necessary for the purpose of affording a just and equitable accounting, particularly where the person charged with its payment is seeking the aid of the court. Barrett v. Joy, 16 Mass. 221, 227. Arnold v. Maxwell, 230 Mass. 441. Goldman v. Worcester, 236 Mass. 319. See Williams v. American Bank, 4 Met. 317, 319.
In the case at bar the plaintiff became the owner of the equity of redemption on January 18, 1918. Although the property was then subject to the three mortgages, he paid no interest which became due after January 1, 1919. It may well be that this omission was for the purpose of forcing the bank to foreclose and thus impair or destroy Mrs. Ryder’s inchoate right of dower. It appears that the bank did institute foreclosure proceedings before Mrs. Ryder brought her bill to redeem. Ryder v. Brockton Savings Bank, supra. In that case it was held against the objection of the plaintiff that Mrs. Ryder was entitled to redeem as hereinbefore set forth. In order to protect her rights she was obliged *65to pay not only the principal, but the interest that had not been paid. In the circumstances it was within the authority of the court to require the plaintiff, if he later wished to redeem, to pay simple interest on the amount paid by Mrs. Ryder to that bank. Such requirement imposes on him only the duty of doing that which equitable considerations enjoin.
The final contention of the plaintiff is that the decree should be reversed because it does not provide that upon redemption the mortgages should be kept alive and held by the plaintiff with the rights of an assignee. The plaintiff is not entitled to the aid of the court to create a right or lien superior to that of Mrs. Ryder. His ownership is now subject to her inchoate dower interest and is subject to an incumbrance created by her husband which she and those claiming under her are not bound to hold or assign for his benefit or in aid of his title. Ryder v. Brockton Savings Bank, supra. Wedge v. Moore, 6 Cush. 8. See Brawn v. Lapham, 3 Cush. 551; McCabe v. Bellows, 7 Gray, 148; McCabe v. Swap, 14 Allen, 188.
G. L. c. 189, § 4, upon which the plaintiff relies, is not pertinent to the questions here involved.
The decree must be modified as herein directed and as may be required in order to bring the account down to the date of the affirmance of the decree; and when so modified it is to be affirmed with costs of this appeal, which are to be paid by the plaintiff.
Decree accordingly.