Continue your plan
Useful next calculations
Rates & sources
A user-entered rate and cash-flow illustration comparing a repayment-mortgage overpayment with an accessible savings alternative. It does not determine lender allowances, savings tax or the value of liquidity.
Source: MoneyHelper — should you pay off your mortgage early? — check the linked guidance and any live quote before acting.
When to use this calculator
- Before buying, renting, refinancing, or reviewing a property investment.
- When you want to compare cash flow, yield, growth, and ownership costs side by side.
- When you need a fast estimate before speaking to an agent, lender, or adviser.
- When you are assessing whether a rental property still makes financial sense after a mortgage rate change.
- When you want to compare the total cost of renting against owning over a five- or ten-year horizon.
A realistic UK planning example
Use these sample inputs as a quick scenario test, then change one variable at a time to compare outcomes.
Mortgage balance (£)
£200,000
Mortgage rate (%)
£200,000
Extra monthly amount (£)
6
After entering these figures, review illustrative first-year interest and extra monthly amount together rather than in isolation — each metric tells a different part of the story. Then rerun the tool with one input adjusted to see which variable has the biggest effect on all three outputs before you settle on a plan.
How to read your results
Illustrative First-Year Interest
Use this metric to compare scenarios side by side and understand how changes in the key inputs drive the final outcome. If the figure surprises you, isolate one variable at a time and rerun the calculation to identify which assumption is responsible.
Extra Monthly Amount
Use this metric to compare scenarios side by side and understand how changes in the key inputs drive the final outcome. If the figure surprises you, isolate one variable at a time and rerun the calculation to identify which assumption is responsible.
Method & assumptionsAuthoritative sources
This planner compares two uses for the same monthly cash: reducing a repayment mortgage balance or accumulating a savings pot. It models fixed entered rates, a chosen comparison period and a one-off early repayment charge, then keeps the mortgage balance and savings value visible side by side.
It also shows the estimated LTV after overpayments and the further amount required to reach a selected milestone. LTV milestones are not promises of a lender rate or acceptance.
The result does not include tax unless you enter a net savings rate, investment returns, offset mortgages, changing rates, annual lender overpayment caps or the value of accessible emergency cash. Check the lender illustration and account terms before acting.
Common mistakes
- !Comparing rent and ownership costs without including taxes, fees, and maintenance.
- !Using purchase price alone without testing the impact of financing or vacancy assumptions.
- !Relying on yield or growth in isolation instead of reviewing the full property case.
- !Forgetting Stamp Duty Land Tax (or its Scottish and Welsh equivalents), which can add thousands to the true cost of purchase.
- !Using optimistic rental growth figures without also testing a flat or declining rent scenario to check downside resilience.
What to do next
- Run a second scenario with a higher rate or lower rental yield to check downside resilience.
- Compare the result with a buy-versus-rent or stamp duty calculator before making an offer.
- Use the related guides below to understand agent fees, legal costs, and ongoing maintenance budgets.
- If you are assessing a buy-to-let, check the gross yield against the net yield after mortgage interest, voids, and management fees.
- Note down the key figures from this scenario to share with your solicitor or mortgage broker so they are working from the same assumptions.
Frequently asked
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