delivered the opinion of the Court:

It is contended by counsel for complainant that, inasmuch as no specified rate of interest is named in the bond or deed of trust, complainant only became liable for the legal rate of 6 per cent interest, as allowed by statute. It is insisted, and not gainsaid, that, at 6 per cent, calculated with a deduction of the principal by partial payments, the indebtedness, principal and interest, was entirely liquidated before the expiration of' the twelfth year, and long prior to the date complainant ceased to make payment of the monthly instalments, as called for in the bond. Complainant, therefore, claims that, having overpaid the amount of the principal indebtedness, with interest thereon at 6 per cent, she should be released from further obligation to defendant.

The obligation named in the bond was not the principal sum of $4,600, but the various monthly payments extending for a period of twenty years. The auditor found that the total of these payments embraced the principal sum with interest at 9 per cent per annum, computed on the baisis of the length of time each instalment had to run. In other words, by the method adopted, the result was the same as if the contract had specifically provided for the payment of $4,600 in monthly payments extending through a period of twenty years, with annual interest thereon at the rate of 9 per cent.

The Revised Statutes of the United States, sec. 714, relating to the District of Columbia, in force at the time this contract was made, provides: “In all contracts made it shall be lawful for the parties to stipulate or agree, in writing, that the rate of 10 per centum per annum, or any less sum, of interest, shall be taken and paid upon every $100 or money loaned or in any manner due and owing from any person or corporation in the District.” The only question presented by this case is whether the *208obligation in writing, providing for the payment of a certain sum of money at definite fixed periods, such sums, by the terms of the contract, being made up of the principal and interest, when no rate of interest is stated, comes within the prohibition of the statute. We think it does not, where the sum payable is fixed, and, by mathematical calculation, it can be readily ascertained that the rate of interest charged therein does not exceed 10 per centum per annum on every $100.

The rule seems to be that, “if the interest has been calculated and included in the principal sum named in the written contract, this is sufficient.” 22 Cyc. Law & Proc. p. 1530, and cases cited. It was held in Cameron v. Merchants’ & M. Bank, 37 Mich. 240, that “the suggestion that the statute requires stipulations for 10 per cent to be in writing, and that unless that rate is expressly mentioned the paper is illegal, is not well founded. The object of the statute was evidently to require the writing to remove the ambiguity that would otherwise exist on the face of an instrument calling for interest, and mentioning no rate. It was to conform to the rule rejecting parol explanations of writings. But where the sum of money to be paid is expressed, there is no ambiguity, and, if it included no more than 10 per cent interest, it is valid.”

The bond in the present case specifically stated that the monthly instalments were payments on the principal sum with interest. The duty was cast upon the complainant of ascertaining the rate of interest therein charged, which she could have accomplished by a simple mathematical calculation before assuming the obligation. She cannot now be heard, after confirming the agreement by payment of the instalments for a long period of years, to assert that she did not know the rate of interest charged. The contract being in writing, and the rate charged being less than 10 per cent per annum, it comes within the provisions of the statute.

The decree is affirmed with costs, and it is so ordered.

Affirmed.