Useful next calculations
When to use this calculator
- Before comparing mortgage products, brokers or repayment types.
- When you want to test how a different deposit, rate or term changes the payment.
- When you need a quick estimate before using a formal illustration or agreement in principle.
- When you are stress-testing your budget against a higher rate.
A worked example
These are the example figures the calculator opens with.
| Input | Value |
|---|---|
| Mortgage balance (£) | £200,000 |
| Current rate (%) | 4.75% |
| Rate to test at deal end (%) | 5.5% |
For those figures the calculator returns:
- Mortgage balance: £200,000.00
- Current rate: 4.75%
- Tested rate: 5.50%
Method & assumptions
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
- Mixing up loan amount and property value, which can distort affordability and LTV.
- Using a headline rate but forgetting fees, insurance, taxes or repayment type.
- Testing only one term length instead of comparing the payment and total cost together.
- Forgetting that a repayment mortgage and an interest-only mortgage produce very different monthly figures.
What to do next
- Run a second scenario with a higher rate or shorter term so you can see the downside clearly.
- Compare the result with an affordability or overpayment calculator before applying.
- Note the monthly payment and total interest for your strongest scenarios before you speak to a broker.
- Check whether a modest overpayment would reduce total interest — use the overpayment calculator next.
Questions people ask
No. You enter every future rate. The calculator shows the payment sensitivity rather than making a rate forecast or product recommendation.