TILA requires that a mortgage lender or servicer send ''an accurate payoff balance within a reasonable time, but in no case more than seven business days'' after receiving the borrower's request. 15 U.S.C. § 1639g.
The formula for calculating simple interest is A = P x R x T. A is the amount of interest you'll wind up with. P is the principal or initial deposit.
Lenders multiply your outstanding balance by your annual interest rate but divide by 12 because you're making monthly payments. So if you owe $300,000 on your mortgage and your rate is 4%, you'll initially owe $1,000 in interest per month ($300,000 x 0.04 ÷ 12).