Lenders look at two things at once: an income multiple and an affordability stress test at a rate higher than you will actually pay. This works out which of the two bites first for your numbers, then shows the buying budget, the monthly payments and the deposit you would need. A guide to the conversation, not a mortgage offer — everything is calculated on your device.
1. Income cap. Household income ร the multiple. Most high-street lenders sit around 4.0โ4.5ร; a handful go higher for professional or high-income cases, and many apply a lower multiple to self-employed income averaged over two or three years.
2. Affordability cap. UK lenders must apply the FCA's responsible-lending rules (MCOB 5A), which means stress-testing whether you could still afford the mortgage at a materially higher rate. This tool takes your net income after tax and National Insurance (a standard band calculation), subtracts your declared debts, childcare and a notional living-cost allowance, then asks how large a loan the stress rate can service over your term. Whichever of the two caps is lower is the borrowing figure shown, and the card tells you which one bit.
3. Payments. Standard capital-and-interest annuity formula,
P = Lยทr / (1 โ (1 + r)^โn), evaluated twice: at the rate you entered and at the stress rate.
Interest-only mortgages would show a much lower monthly figure but never repay the loan, so they are not modelled here.
Nothing is uploaded: no network request is made, and your figures are not stored anywhere — change an input and the answer recalculates on the spot.