The question isn't really how much you need to earn, but what you can afford to repay, how much lenders will lend you and the value of your deposit.

When you're applying for a mortgage, lenders base their decision on what they think you can realistically afford to repay - and that's based on more than just your salary. (They'll also look at your credit rating, but that's not the focus of this article.)

Salary-to-mortgage ratio

Mortgage lenders won't generally lend more than four times your salary. So if you want a mortgage of £120,000, you'd need an annual income of around £30,000. Add your deposit to that and that's the value of the property you could buy on your own (as long as you can actually get a mortgage, that is).

If you're buying with a partner, you could borrow more like three times your combined income to spread the risk - so the mortgage would still affordable if one of you was out of work for a while, for example.

Lenders have to lend responsibly

Mortgage lenders have to work out what you can afford to pay back before they'll lend to you. This is part of what's called 'responsible lending', and the FSA (Financial Services Authority) has rules about it.

Income (what you have coming in every month)

The amount you earn is important because it's going to affect what you can afford to pay back, but that's not the full story.

You need to be able to prove your income and that you really could afford to repay the mortgage you want.

Expenditure (your outgoings)

The mortgage you can afford also depends on what your usual monthly expenditure is - what you spend your money on every month. This includes everything you need for a basic quality of living, like household goods and services, childcare and basic activities.

No one wants to live like a hermit, so it's important that your mortgage leaves you with enough room to still enjoy basic recreation.

Lenders will also look at how much debt you already have on credit cards, overdrafts or loans to try to make sure you don't borrow more than you can afford to repay.

Interest rates

Interest rates can fluctuate, so a mortgage lender will only lend you money based on what you could afford if interest rates did rise.

It is possible to fix the interest you pay on a mortgage, but fixed deals only last for a few years.

Before you move house, you might like to read our guide to the most useful websites for moving house.