Mortgage Payoff Calculator
This mortgage payoff calculator shows how much sooner your mortgage could be paid off if you make an extra monthly payment, a one-time lump sum, or both. It also shows the interest you would save over the life of the loan compared with paying only the regular amount.
Enter the balance still owed, your interest rate (APR), and the number of years left on the loan. Add an extra monthly payment or a one-time extra payment if you plan to make one. The calculator works out your regular payment and compares the schedule with and without the extra money.
Year-by-year schedule
How to use the mortgage payoff calculator
- Enter the balance left on your loan in pounds (£).
- Enter your interest rate (APR) as a percentage.
- Enter the number of years left on your loan.
- Optionally, enter an extra amount you plan to pay each month.
- Optionally, enter a one-time extra payment you could make now.
- Read the time saved, interest saved, new payoff time and your regular payment.
The formula
- Regular payment = the level payment that clears the balance over the years left: P × r ÷ (1 − (1 + r) ^ −n), where P is the amount borrowed, r the annual rate ÷ 12 ÷ 100 and n the number of months
- Each month: interest = balance × annual rate ÷ 12; the rest of the payment reduces the balance
- Extra payments go straight to the balance; the lump sum comes off the balance first
- Time saved and interest saved = the schedule without extra payments − the schedule with them
Worked example
The figures below are made up to show the maths. They are not current prices, rates or product figures.
| Balance left on the loan | £250,000.00 |
|---|---|
| Interest rate (APR) | 6.5% |
| Years left on the loan | 25 years |
| Extra payment every month | £200.00 |
- Time saved 5 years 6 months
- Interest saved £64,927.88
- New time to pay off 19 years 6 months
- Your regular payment £1,688.02
- Interest without extra payments £256,405.37
- Interest with extra payments £191,477.49
Tips for an accurate answer
- Check your current balance and rate with your lender or bank before relying on the figures.
- Ask your lender whether overpayments are allowed and whether there are any charges or limits on them.
- Remember that the calculator assumes the rate stays the same for the whole term, so a change in rate would alter the results.
- Compare a lump sum and a monthly extra payment with the same total amount to see which saves more interest for your loan.
- Treat the result as a guide to the maths only, not as financial advice.
Questions people ask
How can I use an accelerated mortgage payoff calculator?
Enter your balance, interest rate and years left, then add an extra monthly amount to see how it speeds up payoff. The calculator shows the new time to clear the loan and the interest you would save. In the worked example, an extra £200.00 each month cut the term by 5 years 6 months.
Will this calculator show how much my mortgage payment will go up?
No, this calculator does not model rate changes, so it cannot show how much your payment may rise. It works out your regular payment from the balance, rate and years you enter, and shows the effect of extra payments.
Can I use this to work out my mortgage interest rate?
The calculator uses the interest rate (APR) you enter rather than finding one. Enter the rate from your mortgage paperwork or lender, and it will show the interest charged with and without extra payments.
How do I check how an overpayment affects my mortgage?
Enter your balance, rate and years left, then add the overpayment you are considering as a monthly or one-time amount. The results show the time saved and interest saved, which you can check against your lender's figures.
What does this calculator actually tell me?
It shows how many years and months sooner your mortgage would be cleared with your extra payments, and how much interest you would save. It also gives your regular monthly payment and the total interest with and without the extra money.
Do I need to enter an extra payment?
No. Both the monthly extra payment and the one-time extra payment are optional. If you leave them empty, the calculator shows the regular schedule only.
Does the lump sum or the monthly extra go first?
The lump sum comes off the balance first, and each extra monthly payment goes straight to the balance. Both reduce the amount that interest is charged on from that point.
How is the regular payment worked out?
The calculator works out the level monthly payment that clears the balance over the years you have left at your rate. Each month, interest is charged on the balance and the rest of the payment reduces it.
Sources
This calculator uses the standard loan and interest formulas above and the numbers you type. It needs no outside figures.
An estimate from the numbers you enter, worked out with the formula shown. It is maths, not financial advice: your lender or bank has the final figures. Page checked 23 Oct 2026. Read the disclaimer