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Payoff date and total interest

A month-by-month schedule for a fixed-rate loan, with an extra principal payment, the payoff date, total interest, and a CSV of the same rows.

Loan

Added to principal after interest. Use 0 to keep the original term.

How to use it

  1. Enter the loan amount, the annual rate, and the term in years.
  2. Enter an extra monthly principal payment, or leave it at zero.
  3. Set the first payment date. Each later row is one month after the previous row.
  4. Read the payoff date and total interest, scan the schedule, or download the CSV.

Default rate: Freddie Mac Primary Mortgage Market Survey 30-year fixed average, FRED series MORTGAGE30US, as of 2026-10-08, 7.40%. https://fred.stlouisfed.org/series/MORTGAGE30US. Also listed at freddiemac.com/pmms.

Worked example

The form opens on these inputs. Change any of them and build the schedule again. Loan $250,000, rate 7.40%, term 30 years, extra principal $200 a month, first payment 2026-11-01.

The scheduled payment is $1,730.95. Interest each month is the prior balance times 0.074 / 12, rounded to the cent. The $200 extra goes to principal until the last payment, which is only the remaining balance plus that month's interest.

On these inputs the balance reaches zero on the July 1, 2048 payment. That is payment 261. Total interest is $253,006.48. With the extra payment set to $0, the same loan runs 360 payments and pays off on October 1, 2056, with total interest of $373,140.82.

Frequently asked questions

How is the monthly payment calculated?

The scheduled payment is principal times the monthly rate, divided by 1 minus (1 plus the monthly rate) raised to the power of minus the number of months. A 0% rate divides principal by the number of months. Each row rounds interest to the cent.

What does the extra payment do?

The extra amount is added to principal after that month's interest, until the balance is paid off. The schedule stops when the balance reaches zero. The payoff date is the date of that last row.

What does the CSV contain?

One header row and one row per payment: payment number, date, payment amount, extra principal, interest, principal, and remaining balance.

Which rate fills the form?

The rate field starts at the Freddie Mac Primary Mortgage Market Survey 30-year fixed average, published as FRED series MORTGAGE30US. That observation is 7.40% as of 2026-10-08. The field is editable.

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