It estimates the effect of adding a regular overpayment to a repayment mortgage while holding the entered rate constant. It does not include early repayment charges, changing mortgage deals, remortgaging costs or lender-specific overpayment caps.
MORTGAGE OVERPAYMENT
Mortgage overpayment calculator
Estimated monthly repayment
£1,667/month
- Mortgage amount
- £300,000
- Loan-to-value
- 85.7%
- Total interest
- £200,249
- Paid off in
- 25y 0m
- Overpayment saving
- £0
Compare your normal repayment with a regular monthly overpayment and estimate the time and interest saved. This is the quick check users want when deciding whether spare cash should go into the mortgage or somewhere else.
It estimates the effect of adding a regular overpayment to a repayment mortgage while holding the entered rate constant. It does not include early repayment charges, changing mortgage deals, remortgaging costs or lender-specific overpayment caps.
Small overpayments can look insignificant month to month but still cut a meaningful amount of interest over the life of the mortgage. The useful question is whether the overpayment shortens the term enough to matter relative to your savings goal and emergency fund.
- Overpayment limits, product fees, rate changes and whether the mortgage is repayment or interest-only all change the savings.
- Some lenders also apply overpayments differently across fixed-rate and tracker products.
How this fits the mortgage cluster
Overpayment is usually the next step after you know the mortgage payment and affordability range. If the payment is too high, check rate rise or shorter term first. If you still have room after keeping an emergency fund, this page shows how much faster you could clear the balance.
SOURCES & REVIEW
Checked against official guidance
Last reviewed 1 September 2026 · Rule version GB-2026.27.1
Daily/weekly source monitoring. If a source changes, the affected rule set is reviewed before publication.
All source links are kept visible so you can verify the figures used on this page.
Source line: Overpayment guidance and repayment effects are checked against MoneyHelper guidance and current mortgage rule data.
MoneyHelper: Paying off your mortgage early ↗Sources, methodology and update policy →Report an issue or correction →WHY RESULTS DIFFER
Why two users can see different results
Why the result can differ
Different tax codes, payroll periods, Scottish bands, pension methods or lender assumptions can change the outcome.
One-off bonuses, pay frequency, overpayments, allowances and reliefs can move the result away from a simple annual estimate.
Where a rule depends on eligibility or legal status, this page shows an estimate and links to official guidance.
This section is intentionally repeated on key tools so the explanation stays near the result instead of being hidden in a separate policy page.
COMMON QUESTIONS
Frequently asked questions
Can I overpay without a charge?
Many mortgages limit penalty-free overpayments. Check the lender’s annual allowance and early repayment charge terms.
Does the saving assume a fixed rate?
Yes. This estimate holds the entered rate constant, so remortgaging or variable-rate changes will alter the result.
Should I overpay instead of saving?
Not always. Compare the mortgage rate with your savings rate, emergency fund needs and any overpayment restrictions.
Does a small extra payment really matter?
Yes. Even modest monthly overpayments can cut term length and total interest over time.
Should I overpay before remortgaging?
It depends on fees and product terms. A cheaper refinance can sometimes beat extra overpayment.
Does this work for interest-only mortgages?
No. It is aimed at repayment mortgages where overpayments reduce the capital balance.