National Loan Monthly Payment Calculator
Calculate your fixed monthly payment for any standard amortizing loan — mortgage, auto, personal, or student loan — using the standard amortization formula.
Formula
Standard Amortization Formula:
M = P × [r(1 + r)n] / [(1 + r)n − 1]
- M = Fixed monthly payment
- P = Loan principal (initial balance)
- r = Monthly interest rate = Annual rate ÷ 12
- n = Total number of monthly payments = Years × 12
Total Payment = M × n
Total Interest = Total Payment − P
New payoff term with extra payments:
nnew = −ln(1 − P·r / (M + extra)) / ln(1 + r)
Assumptions & References
- Assumes a fixed interest rate for the entire loan term (fully amortizing loan).
- Payments are made monthly at the end of each period.
- Interest is compounded monthly (annual rate divided by 12).
- Extra monthly payments are applied entirely to the principal, reducing the outstanding balance and shortening the loan term.
- At 0% interest, the monthly payment equals the principal divided by the number of months.
- Formula source: Consumer Financial Protection Bureau (CFPB) — standard mortgage amortization; also defined in Investopedia: Amortization Formula.
- Applicable to mortgages, auto loans, personal loans, and student loans with fixed rates.
- Does not account for taxes, insurance, PMI, origination fees, or variable-rate adjustments.