Mortgage Calc

Fixed-rate, fully amortizing loan with monthly payments. The annual nominal rate is divided by 12. Term may be entered in years or whole months; changing units converts the value. First payment is the first scheduled instalment, not the loan disbursement date.

All amounts use the same freely chosen currency. No taxes, insurance, fees, variable rates, interest-only periods or early-repayment penalties. This is not an APR calculation or a binding bank schedule.

Extra monthly principal and a one-off principal payment are applied after that month’s interest, without recasting the normal payment. Payments are capped at the remaining debt. A lump sum scheduled after an accelerated payoff is not paid and is flagged. Month numbering starts at 1; month 1 coincides with First payment. Disable extras to exclude their fields.

Interest, paid totals and payoff dates come from the actual monthly ledgers. Values are calculated without monthly cent rounding; displayed money is normally rounded to two decimals, with scientific notation for tiny or very large values. A bank’s cent-rounded/day-count schedule may differ. Stable principal shares avoid a spurious balloon payment at high rates.

The expandable plan switches between standard and extra-payment schedules. Initially 50 rows; Show more adds 100. Copy/CSV always includes the entire selected plan, including applied lump payments. CSV has decimal points and ISO year-month dates; downloads are UTF-8 with BOM. No input is uploaded.

Software bounds: positive loan up to 10¹², nominal rate 0–1000%, 1–1200 whole months, four-digit payment years. Extra amounts are nonnegative and capped when applied. Zero interest is supported. Numerically unresolvable cases show an error.

M = P·i / (1−(1+i)⁻ⁿ), with i = r/1200 for nominal annual r in percent and n monthly payments. At zero interest M = P/n.