Rates & sources
Standard amortisation formulas used across UK lenders. Interest rates move daily — confirm with your lender or broker.
Source: Bank of England — Statistics — figures refreshed at the start of each tax year.
When to use this calculator
- Before comparing lenders, brokers, or repayment options.
- When you want to test how a different deposit, rate, or term changes affordability.
- When you need a quick estimate before using a formal quote or agreement in principle.
- When you are stress-testing your budget against a potential rate rise to see the impact on monthly payments.
- When you want to understand the full cost of borrowing — not just the monthly figure — before you commit.
A realistic US planning example
Use these sample inputs as a quick scenario test, then change one variable at a time to compare outcomes.
Gross Monthly Income ($)
$55,000
Mortgage / Rent Payment ($)
$280,000
Car Loan Payments ($)
$280,000
Student Loan Payments ($)
$280,000
After entering these figures, review front-end dti, back-end dti and max mortgage (conv.) 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
Front-End DTI
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.
Back-End DTI
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.
Max Mortgage (Conv.)
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.
Max Total Debt
This is the headline outcome of the calculation, but it is most useful when read alongside the supporting metrics below it rather than in isolation. Try changing one input at a time and watching how this total moves to understand which driver has the biggest impact.
Remaining Capacity
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 calculator computes your front-end and back-end debt-to-income ratios using gross monthly income as the denominator, consistent with how Fannie Mae, Freddie Mac, FHA, and VA underwriting guidelines define DTI. The front-end ratio isolates housing costs only; the back-end ratio adds all recurring monthly debt obligations. The conventional maximum benchmarks used here are 28% front-end and 36% back-end, the traditional Fannie Mae/Freddie Mac standard. FHA generally permits a 31/43 split, while VA and USDA use a single 41% back-end guideline. Automated underwriting systems can approve loans above these thresholds with compensating factors, so these figures should be treated as general guidance rather than definitive approval thresholds.
The calculator does not include property taxes, homeowners insurance, or HOA fees in the proposed mortgage payment — you should add those estimates to your housing figure for a more accurate front-end DTI. It also assumes all income is fully documented and does not adjust for self-employment, commission, or variable-income verification requirements that apply under agency guidelines. Verify current DTI limits directly with your lender or loan officer, as guidelines change and vary by loan program and underwriting method.
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 and total costs.
- !Not accounting for the impact of a rate revert after an introductory fixed period ends, which can sharply increase payments.
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.
- Use the related guides below to understand trade-offs before you request live quotes.
- Note down the monthly payment and total interest for your two or three strongest scenarios so you have a clear comparison ready when you speak to a broker.
- Check whether making a modest overpayment each month would reduce total interest significantly — run the overpayment calculator next to find out.
Frequently asked
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End-of-article next steps
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