Continue your plan
Useful next calculations
Rates & sources
A user-entered mortgage-payment sensitivity model. It carries the estimated balance to the chosen deal-end month, then tests the rates entered without forecasting products or market rates.
Source: MoneyHelper — mortgage calculator guidance — 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
Current rate (%)
5%
Rate to test at deal end (%)
5%
After entering these figures, review mortgage balance, current rate and tested rate 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
Mortgage Balance
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.
Current Rate
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.
Tested Rate
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 mortgage rate-shock planner carries an entered balance forward to the end of the current deal, using the current rate and remaining term. It then recalculates the payment at a rate you enter and a separate higher stress rate.
The monthly housing budget you enter is compared with both future payment scenarios to make any headroom or shortfall clear. It is a planning estimate, not a lending decision.
It does not predict rates, compare live products, account for fees, model lender affordability criteria or include non-mortgage home costs. Use current lender illustrations and regulated mortgage advice where appropriate.
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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