Loan Amortization Schedule

Month-by-month principal / interest / balance with optional extra-principal payment, total interest, payoff month.

Run the calculator

Example

You enter

Principal (USD) 250000
Annual rate (percent) 6.5
Term (months) 360

You get

Payment $1580.17
Total interest $318861
Payoff in (months) 360

Details, formula, and sources

Payment P = (r * PV) / (1 - (1+r)^-n) where r is monthly rate and n is term in months. Schedule recurrence: interest_i = balance_(i-1) * r; principal_i = P - interest_i + extra; balance_i = balance_(i-1) - principal_i.

Standard mortgage / installment-loan formula. First principles.

No code citation required (arithmetic). Cross-check against any published mortgage calculator.

Estimate. Verify before sending to your bookkeeper, banker, or CPA.

Field names used by the API: principal, annual_rate_pct, term_months, payment, total_interest, payoff_month

Compounding monthlyconvention; APR / APY conversion is the user's responsibility
Extra principal applied to principal each period after interest accruesuser input; no escrow / fees