A mortgage calculator starts from a price you already picked and tells you the payment. This one runs the other way: it starts from what you earn, subtracts what you already owe, keeps back the taxes and insurance, and only then asks how much loan that leftover payment supports. The number that comes out is a starting point for house-hunting rather than a verdict on a house you have already fallen for.

Using it in three steps

1. 1 Enter your gross monthly income and the debt payments you already make.
2. 2 Add your saved deposit, the rate you expect and how long a loan you want.
3. 3 Move the income share up and down. It changes the answer more than the interest rate does.

Why the percentage matters more than the rate

People shopping for a mortgage spend weeks chasing a quarter point of interest and minutes deciding what share of their income to commit. The second choice moves more money. At a typical rate, dropping the housing share from 33% to 28% cuts the reachable price by roughly a sixth — far more than a quarter-point rate difference ever will, and unlike the rate, it is entirely yours to set.

What a lender approves is not what you can live with

Lenders assess whether you will repay, not whether you will be happy. Their limits leave room for the loan and nothing else — not childcare that starts next year, not the commute that comes with the cheaper suburb, not the roof that fails in year three. The share of income you type here is the one place in this calculation where your own life enters the maths, which is why it is a field and not a fixed rule.