Is this calculator “exact”? It’s deterministic using stated assumptions, but it won’t cover every edge case (e.g., special reliefs). Use it for planning and compare with official guidance for edge cases. Why do results change sharply at thresholds? Most UK taxes/charges are banded. Crossing a band can change the marginal rate applied to the next slice, which can look like a step-change in totals.

Mortgage Overpayment Calculator | Sterling Calculators

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Interest (no overpay)

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Interest (with overpay)

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About this calculator

Estimate how much time and interest you could save by making a fixed monthly overpayment on your mortgage. Enter your balance, interest rate, term and overpayment to see an estimated new payoff time and interest saved. This is a planning tool to help you compare overpayment scenarios and understand the effect of rate changes.

How the calculation works

We amortise the loan month‑by‑month using your interest rate and scheduled payment, then apply the additional overpayment to reduce the balance faster. We compare total interest with and without the overpayment.

FAQ

Will my lender allow overpayments?

Many lenders do, but there may be annual limits or early repayment charges (ERCs).

Is it better to overpay or invest?

It depends on rates, risk tolerance, and liquidity needs.

Does this include ERCs/fees?

No. Add those separately when deciding.

Is the result exact?

It’s an estimate; real schedules can vary by lender calculation method.

Related calculators

Understanding your mortgage overpayment result

This tool estimates the impact of regular or one-off overpayments on mortgage interest and term, based on the inputs you provide. It’s a planning model to compare scenarios.

Interest is calculated on the remaining balance using the stated rate.
Overpayments reduce principal faster, reducing interest paid over time.
Outputs focus on interest saved and term reduction (where applicable).

Next steps

Before overpaying, compare interest saved versus alternative uses of cash and any ERCs.

Stamp Duty (property) → VAT calculator →

FAQs

Does this include fees or early repayment charges?

No—fees and ERCs vary by lender and must be considered separately.

Is the repayment schedule exact?

It’s a planning estimate. Lenders may calculate interest daily and apply different rounding.

Can overpayments shorten term or reduce monthly payment?

This model assumes the standard approach used in the calculator; check lender options.

Assumptions: England/rUK bands; annualised calculations; excludes student loans/benefits-in-kind unless stated. Tax core: /assets/tax-core.js.

Mortgage Overpayment Calculator (UK)