HAMMOND v. HAMMOND. 383

Interest is always allowed on debts secured by a mortgage; and
where an account is stated, with the knowledge of the mortgagor,
and the whole amount, principal and interest, is paid by an as-
signee of the mortgagee, with the assent of the mortgagor; such
aggregate amount of principal and interest, shall bear interest in
favour of the assignee. And so too, where the principal and inte-
rest has been paid by a surety, he shall have interest upon the
whole, (m) Such a conversion of interest into principal in favour
of an assignee of a mortgagee, a surety, and the like, is founded
upon an express, or implied contract between the parties, as to a
separate or single transaction; and is not considered illegal, as it
would be, if done under an original contracting, for the compound-
ing of interest, or for a periodical conversion of the interest into
principal, (n)

On a bill for an account and the like, by a creditor to obtain
payment from his debtor; or on a bill to recover a legacy, the sub-
sequent interest is computed, not upon the aggregate amount found
due at the time of the decree; but on the principal only, from the
time the debt was liquidated, or became payable until it is paid or
brought into court, (o) The rule for computing interest, in all
cases, where the debt carries interest; and the debtor has made par-
tial payments, is, that the interest is calculated from the time the
debt became payable, down to the day of the first payment: and the
interest is added to the principal, then the payment is deducted
from the whole; and if such payment satisfies the whole interest
and a part of the principal, then the interest is calculated upon the
balance of the principal to the day of the second payment, from the
whole of which the second payment is deducted, &c. But if the
first payment does not discharge the whole interest, then after apply-
ing it to the satisfaction of so much of the interest, the interest is
calculated upon the principal only, until the day of the second pay-
ment, which is deducted from the whole amount, and so on. So
that in no way is any interest calculated and paid upon interest, (p)

But where the estate of the deceased, or insolvent debtor is in-

(m) Powel Mortg. 908, 905; 2 Fonb. 438.—(n) Ossulston v. Yarmouth, 2 Salk.
449; Perkyns v. Baynton, 1 Bro. C. C. 574; Ex parte Bevan, 9 Ves. 224; Cham-
bers v. Goldwin, 9 Ves. 271; Caliot v. Walker, 2 Anstr. 495; Eaton v. Bell, 7 Com.
Law Rep. 14.—(o) Butler v. Duncomb, 1 P. Will. 453; Bickham v. Cross, 2 Ves.
471; Perkyns v. Baynton, 1 Bro. C. C. 574; Creuze v. Lowth, 4 Bro. C. C. 158,
318; Turner v. Turner, 1 Jac. & Walk. 47; Parker v. Mackall, ante 68; Wood-
ward v. Chapman, ante 71; Sloss v. Mcllvane, ante 73; Craig v. Baker, ante 238.—
(P) Frazier v. Hyland, 1 H. & J. 98; Gwinn v. Whitaker, 1 H. & J. 754.