Estimate interest savings, time saved, and your balance over time when you add a regular monthly overpayment.
No account needed
Runs in your browser
Built for quick comparisons
Example scenario
£38,458
Estimated interest saved with a £200 monthly overpayment on the default mortgage.
Inputs
Private
Runs in browser
These optional prompts do not change the calculation, but they help you decide whether the overpayment estimate is realistic for your mortgage product and cash position.
If you do not know the allowance, leave it blank and check your mortgage offer or lender statement before acting.
Try a scenario
Estimate
Estimated interest saved
£38,458
Estimated time saved
5 years 1 months
Current payment
£1,390
With overpayment
£1,590
+£200/month
Current term
25 years
New term
19y 11m
Assumes the rate stays the same and every overpayment reduces the balance immediately.
Assumptions
Check these inputs before relying on the result.
Last reviewed
12 June 2026
Interest method
Monthly interest is estimated from the annual rate unless a page states a different method. Lender figures can use daily interest, product-specific rules, and exact payment dates.
Educational scope
UK-focused calculator estimate. It explains trade-offs and does not make a personal recommendation.
Results are estimates based on the assumptions shown here. They are not financial advice and can differ from lender figures because real products, fees, rate changes, overpayment rules, and repayment timing vary.
Learn the maths
Follow the step-by-step lesson to see how overpayments reduce the balance, why that can save interest, and how the mortgage freedom date estimate is worked out.
Projection
What this estimate suggests
Use the result as a comparison point, then check overpayment limits, cash buffer, and whether remortgaging could change the trade-off.
Recommended next steps
A short follow-up can help put this estimate into context before you make a money decision.
Before committing spare cash to the mortgage, compare the estimated interest saving with a possible investment route and the risk that comes with it.
Open next step
Use the dashboard as a secondary checkpoint if you want to update the balance, LTV, payment, or mortgage-free estimate before comparing alternatives.
Open next step
This calculator provides estimates only and does not constitute financial advice. Mortgage calculations may vary depending on lender terms, overpayment limits, interest rate changes, fees, and repayment structures. Always consult a qualified financial advisor or your mortgage provider before making financial decisions.
Calculator guide
Use the calculator to compare your current repayment path with a regular monthly overpayment. The most useful inputs are your current outstanding balance, the interest rate you want to model, the years left on the mortgage, and the extra amount you could comfortably pay each month.
The result is an estimate, not a lender statement. It is best used for comparing scenarios: for example, whether an extra payment of 50, 100, or 250 a month could make a meaningful difference before you commit real cash.
Step 1
Enter the outstanding balance, interest rate, and years left. The calculator estimates the standard monthly repayment for that remaining term.
Step 2
The overpayment is applied alongside the estimated standard repayment, reducing the balance sooner than the base schedule.
Step 3
The result compares the base repayment path with the overpayment path, showing estimated interest saved and how much earlier the balance could reach zero.
Check whether your mortgage has an overpayment allowance, early repayment charge, or a specific process for choosing whether overpayments reduce the term or the required monthly payment.
It is also worth comparing overpayments with other uses of cash, such as emergency savings, high-interest debt repayment, pension contributions, or investing.
Common questions
Earlier payments usually reduce the balance sooner, which can reduce future interest. A lump sum can be powerful if you have spare cash, while monthly overpayments may be easier to budget. The best choice depends on your lender rules, emergency savings, and other debts.
They can. Some mortgage deals allow overpayments up to a set limit, while payments above that limit may trigger an early repayment charge. Always check your mortgage offer or ask your lender before making large overpayments.
Not always. Mortgage overpayments can offer a clear interest saving, but you may want emergency savings first and may prefer to repay higher-interest debts before overpaying a mortgage. Investing adds risk and may perform better or worse than the mortgage interest saved.
It depends on how your lender applies overpayments. Some borrowers choose to keep the monthly payment similar and shorten the term; others reduce the required monthly payment. Check your lender's process before assuming which outcome will apply.
Keep learning
Understand allowances, early repayment charges, and lender restrictions.
Read guide →
See why payment size, interest rate, and timing affect potential savings.
Read guide →
Compare certainty, risk, liquidity, and long-term return potential.
Read guide →
Compare monthly, annual, and occasional overpayment patterns.
Read guide →
Before making a real overpayment, compare the estimate with your lender's terms and independent guidance.
Tune your overpayment
Jump back to the calculator.
Learn This Calculation
Use the education page before relying on the result. It explains the assumptions, shows the maths, gives worked examples, and includes practice questions so the estimate is easier to check.
Learn how extra payments reduce the balance used for future interest estimates.
Covers amortisation, monthly interest, balance updates, interest saved, and mortgage-free dates.
Works through a £200,000 mortgage with a £200 monthly overpayment.
Practise estimating interest saved, time saved, and why lender limits matter.
Next Lesson
Check the opportunity cost before treating overpayment as the only sensible use of spare cash.
OverPayWise provides educational estimates only. It is not FCA authorised, does not provide regulated financial advice, and does not arrange mortgages.