Short answer
A fully amortizing loan's payment is P × r / (1 − (1 + r)^−n), where P is the amount, r the rate per payment period and n the number of payments. For example, $100,000 at 6% over 60 monthly payments is $1,933.28 a month, with $15,996.81 of total interest.
How it's calculated
The year-by-year table applies each payment to interest on the outstanding balance first, then to principal, and adds up the twelve months (or 52 weeks, and so on) of each year. The final payment is adjusted for rounding so the balance ends at zero.
APR including fees treats any up-front fee as reducing what you receive and finds the yearly rate at which your payments equal that smaller amount. With no fee, the APR equals the note rate.
Checking the math
The default example and others are covered by automated tests: $100,000 at 6% for 60 months gives $1,933.28; $200,000 at 7.5% for 120 months gives $2,374.04; $10,000 at 0% for 12 months gives $833.33.
Using the result
- Multiply the payment by payments per year to get yearly debt service, then test it in the DSCR calculator.
- Compare offers with the same term on APR; compare different terms on both APR and total interest.
- For SBA 7(a) loans, SBA caps the rate a lender may charge; see SBA loans explained.