Property
Mortgage Overpayment Calculator
Enter your mortgage balance, rate, remaining term, and overpayment plan to compare your current payoff path with an overpayment scenario.
Inputs
Results
Useful next checks
- Check the inputs before relying on the result.
- Try a second scenario to compare outcomes.
- Read the guide below for context.
Intro
Use this mortgage overpayment calculator to estimate how much time and interest you could save by paying extra toward your mortgage. Enter your current balance, rate, remaining term, and planned overpayments to compare your current payoff path with a faster one.
What this mortgage overpayment calculator does
The calculator compares two repayment scenarios:
- Your current mortgage repayment path.
- The same mortgage with a monthly overpayment, a one-off overpayment, or both.
It shows the estimated new payoff time, time saved, interest saved, and total interest under each scenario.
How it works
The calculator models the mortgage month by month. Each month it adds interest, applies your normal payment, then applies any extra overpayment from the selected start month.
If you leave the current monthly payment as zero, the calculator estimates a standard repayment using the mortgage balance, annual interest rate, and remaining term. If you enter your own monthly payment, that payment is used for both the current and overpayment scenarios.
Example calculation
Suppose you have a mortgage balance of 200,000, an interest rate of 5%, and 25 years remaining. The standard monthly repayment is estimated from those inputs.
If you add a 200 monthly overpayment from the first month, the calculator reduces the balance faster. Because the balance falls sooner, less interest is charged in later months, which can shorten the mortgage and reduce total interest.
How to use the result
Use the result to test different overpayment plans before speaking to your lender. Try smaller and larger monthly overpayments, or compare a one-off lump sum with a regular payment.
Before making an overpayment, check whether your mortgage has an annual overpayment allowance, early repayment charge, product fee, or minimum overpayment amount.
Assumptions and limitations
- The calculator assumes a fixed interest rate for the full term entered.
- It does not include early repayment charges or lender fees.
- It assumes overpayments reduce the balance rather than lowering future monthly payments.
- It does not model offset mortgages, interest-only mortgages, or payment holidays.
- The result is an estimate, not a lender statement.
FAQs
- Should I overpay monthly or as a lump sum? Earlier overpayments usually save more interest because the balance falls sooner, but fees and cashflow matter.
- Does this change my contractual payment? The calculator assumes your normal payment stays the same and the extra amount reduces the balance.
- What if my rate changes later? Run a separate scenario with the new rate and remaining term.
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Frequently asked questions
Does this include early repayment charges?
No. Check your mortgage deal for overpayment limits, early repayment charges, and product fees before acting.
What if I enter my current monthly payment?
The calculator uses that payment for both scenarios. If you leave it as zero, it estimates a standard repayment from the remaining term.
When is the lump sum applied?
The one-off overpayment is applied in the selected start month before that month's interest is calculated.