Mortgage overpayment calculator

Calculations run in your browser.

Interest saving after entered charges

£41,842.60

Mortgage overpayments breakdown
Original monthly payment	£1,169.18
Payment with monthly overpayment	£1,369.18
Lump sum paid now	£0.00
Original interest over remaining term	£150,754.02
Interest with overpayments	£108,911.43
Additional charges entered	£0.00
Time saved	74 months
New repayment term	18 years 10 months

Mortgage balance over time

OriginalWith overpayments

Projection values

Mortgage balance over time
Scenario	Month	Balance
Original	0	£200,000.00
Original	12	£195,876.19
Original	24	£191,541.39
Original	36	£186,984.82
Original	48	£182,195.12
Original	60	£177,160.38
Original	72	£171,868.05
Original	84	£166,304.95
Original	96	£160,457.23
Original	108	£154,310.33
Original	120	£147,848.95
Original	132	£141,056.99
Original	144	£133,917.54
Original	156	£126,412.82
Original	168	£118,524.15
Original	180	£110,231.88
Original	192	£101,515.36
Original	204	£92,352.88
Original	216	£82,721.64
Original	228	£72,597.64
Original	240	£61,955.68
Original	252	£50,769.26
Original	264	£39,010.51
Original	276	£26,650.17
Original	288	£13,657.45
Original	300	£0.00
With overpayments	0	£200,000.00
With overpayments	12	£193,420.42
With overpayments	24	£186,504.21
With overpayments	36	£179,234.15
With overpayments	48	£171,592.15
With overpayments	60	£163,559.16
With overpayments	72	£155,115.19
With overpayments	84	£146,239.22
With overpayments	96	£136,909.13
With overpayments	108	£127,101.70
With overpayments	120	£116,792.50
With overpayments	132	£105,955.86
With overpayments	144	£94,564.79
With overpayments	156	£82,590.94
With overpayments	168	£70,004.49
With overpayments	180	£56,774.09
With overpayments	192	£42,866.79
With overpayments	204	£28,247.98
With overpayments	216	£12,881.23
With overpayments	226	£0.00

Constant interest rate, monthly compounding and payments at month end. Lump sum is paid immediately; the original scheduled payment is retained so the term shortens. Charges are paid separately, not financed. Check your lender’s overpayment allowance and early repayment charges. Investment returns and future rate changes are not modelled.

Calculation details

How overpayments change the term

The scheduled repayment is calculated from the balance, rate and remaining term. A lump sum reduces the balance immediately, while regular extra payments reduce it each month. The scheduled payment stays unchanged, shortening the term.

Example

£200,000 at 5% over 25 years has a scheduled repayment of about £1,169.18. Adding £200 monthly clears it in 226 months, 74 months earlier, saving about £41,842.60 interest before charges.

Limits

Constant interest rate and monthly interest model. Lender daily interest, rate changes, early repayment charges and whether the lender reduces payments rather than the term can change the outcome. Check the specific overpayment allowance; it is not always 10%.

Sources

Checked 2026-10-25. Estimate only, not financial advice.

Interest saving after entered charges£41,842.60