Loan Payoff & Extra Payment Calculator Guide

What This Calculator Does

Keep the existing equal-installment, equal-principal and interest-only monthly modes, and add monthly extra principal or a one-time principal payment in a selected period. Compare the actual schedule with the same loan without extras: payoff month, months saved, interest saved and adjusted final payment.

When to Use It

Compare cash-flow burden and early principal repayment for a fixed-rate loan. For taxes, insurance, PMI and HOA use the mortgage budget calculator. Principal here is the amount borrowed, rather than a home’s purchase price.

Inputs Explained

Principal is 1000–1 trillion, nominal annual rate 0–30%, and term 1–30 years with years×12 a whole number. Zero interest works. Extra principal is 0–1 trillion; its selected one-time period is a whole number from 1 through the original month count. Enter a valid first-payment month in years 0001–9999; the final month must remain in range. Loan-type choices label scenarios rather than impose lender eligibility or policy.

How the Calculation Works

Monthly rate r = annual percentage/1200 and n = years×12. Equal installments use M = P·r/[1−(1+r)^−n], or P/n at zero rate. Equal principal uses P/n scheduled principal plus interest on the opening balance. Interest-only pays opening-balance interest until the final original period. Each month accrues interest first, pays scheduled principal, then applies monthly extra and the selected one-time extra. Principal cannot exceed the remaining balance. The smaller balance changes next month’s interest, not interest already accrued this month.

Example

Borrow 1200 at 0% for one year and add 100 monthly. The scheduled payment is 100 and each actual payment is 200, finishing in six months instead of twelve. A first payment in 2026-11 gives payoff in 2027-04 versus 2027-10. Interest savings are zero because the baseline is interest-free. With 150 extra monthly, four payments of 250 leave an adjusted final payment of 200.

How to Understand the Result

The equal-installment headline excludes extra principal; other modes show the actual first payment. Every schedule row includes extras. Payoff is a month estimate, not a day-specific contractual deadline. This model retains scheduled principal rules instead of recasting to a lower payment; lender recasting or penalties would change the result.

Common Mistakes

Monthly extras are not payments every fourteen days. A one-time extra occurs once. Oversized extras pay only the remaining principal; no negative balance or surplus cash is created. If the loan finishes before the selected one-time period, that extra never occurs.

FAQ

When do extra payments take effect?

Monthly extra principal follows that month’s payment; a one-time extra follows the selected payment. The lower balance affects the next month’s interest.

Is this a true biweekly loan calculator?

No. Interest and payments are monthly; a payment every 14 days is not modeled.

What if extra principal exceeds the balance?

Only remaining principal and current interest are paid. The final payment is reduced and the balance cannot go negative.

Notes

Fixed nominal rate and monthly accrual/payment only. No fees, penalties, daily accrual, variable rates or lender calendars. Floating-point calculations display currency to two decimals. Confirm the contract and lender’s settlement schedule. Inputs, including extras, restore from share URLs; consider financial privacy before sharing.