Mortgage payoff calculator
See how extra monthly payments or a lump sum shorten your mortgage and cut interest.
About the mortgage payoff calculator
See how extra monthly payments or a lump sum shorten your mortgage and cut interest.
Part of SmartCalcy’s mortgage & real estate tools. It runs in your browser with no account, uses your own currency and units (change them at the top of the page), and gives estimates for information only, so check official guidance before you rely on a result.
How to use the mortgage payoff calculator
What it calculates and when to use it
This calculator shows how much sooner you could be mortgage-free, and how much interest you would save, if you overpay each month or make a one-off lump sum.
How to use it, step by step
- Enter your current balance, interest rate and the years remaining.
- Add the extra amount you can pay each month and any lump sum you could pay now.
- Compare the new payoff time and interest with the original plan.
What each input means
- Mortgage balance now – What you still owe, not the original loan.
- Interest rate – Your current yearly rate.
- Years left – The remaining term on the mortgage.
- Extra each month – Money added to each regular payment.
- Lump sum – A one-off payment applied immediately to the balance.
How to read the results
- Mortgage-free in – How long the loan lasts with your overpayments.
- Interest saved – Interest without extra payments minus interest with them.
- Payment you make now – The required payment plus your extra amount.
The formula
The required payment is P × r ÷ (1 − (1 + r)^−n). Each month interest = balance × r, and the whole payment plus extra, minus that interest, reduces the balance. The loop runs until the balance reaches zero.
A worked example
A 200,000 balance at 5.5% with 25 years left has a required payment of 1,228.17. Paying 200 more each month clears it in 18 years 9 months, 6 years 3 months sooner, and cuts interest from 168,452 to 120,683, a saving of about 47,770.
Assumptions and limits
- A fixed rate for the rest of the term.
- Overpayments are accepted without charge. Many lenders cap penalty-free overpayments, often at 10% of the balance a year.
- The lump sum is paid immediately.
Common mistakes
- Overpaying while carrying higher-rate debt such as credit cards. Clear the dearest debt first.
- Using up emergency savings for overpayments.
- Forgetting that a fixed deal may carry an early repayment charge.
Frequently asked questions
Is overpaying always better than investing?
Overpaying earns a guaranteed return equal to your mortgage rate. Investing might earn more but is not guaranteed, so the answer depends on the rate and your risk tolerance.
Does a lump sum or monthly overpayment save more?
Money paid earlier saves more interest, so a lump sum now generally saves more than the same total spread over years.
Related tools
Details
- Payment you make now
- £1,428.17 a month£1,228.17 required
- Interest without extra payments
- £168,452.50
- Interest with extra payments
- £120,682.73
- Interest saved
- £47,769.76
- Original payoff time
- 25 years
Year by year
| Year | Principal | Interest | Balance |
|---|---|---|---|
| 1 | £6,295 | £10,843 | £193,705 |
| 2 | £6,650 | £10,488 | £187,054 |
| 3 | £7,025 | £10,113 | £180,029 |
| 4 | £7,422 | £9,716 | £172,607 |
| 5 | £7,840 | £9,298 | £164,767 |
| 6 | £8,283 | £8,855 | £156,484 |
| 7 | £8,750 | £8,388 | £147,734 |
| 8 | £9,243 | £7,895 | £138,491 |
| 9 | £9,765 | £7,373 | £128,726 |
| 10 | £10,316 | £6,822 | £118,411 |
| 11 | £10,898 | £6,241 | £107,513 |
| 12 | £11,512 | £5,626 | £96,001 |
| 13 | £12,162 | £4,977 | £83,839 |
| 14 | £12,848 | £4,291 | £70,992 |
| 15 | £13,572 | £3,566 | £57,419 |
| 16 | £14,338 | £2,800 | £43,081 |
| 17 | £15,147 | £1,991 | £27,935 |
| 18 | £16,001 | £1,137 | £11,934 |
| 19 | £11,934 | £263 | £0 |