I'm buying a flat with my boyfriend – how do we split ownership fairly?

Q My boyfriend and I are going to buy a flat together. The purchase price of the flat is £360,000. I’m going to contribute a large deposit of £200,000 and my boyfriend is going to put in £30,000 in cash for all the buying costs including stamp duty, solicitor fees, furniture and so on, and is going to take out a £160,000 mortgage on his own.

I think I should own 51.3% of the flat – 200 divided by (200+160+30) times 100. However, my boyfriend disagrees and has suggested that we should take the interest he will pay on his mortgage (around £80,000 in total) into account. Which means after he finished paying his mortgage, he will own a bigger percentage than me.

How do people split homeownership fairly in this scenario? SS

A Not in the way either you or your boyfriend propose is the short answer. When determining the percentage share of the flat that you each own, you certainly shouldn’t take into account the mortgage interest that your boyfriend will end up paying. That would be like taking into account your loss of interest on the £200,000 you are contributing towards the purchase, which would be a nonsense.

Your suggested calculation is on the right lines because it takes into account the full cost of buying the flat – including the purchase price plus fees and stamp duty – and the cash contribution that each of you will make to the purchase. Yours is from savings and your boyfriend is raising the cash by a combination of cash set aside and a mortgage. However, I don’t think you should include the amount your boyfriend will spend on furniture for the flat because it’s not part of the purchase price.

To work out your respective shares, you can use your calculation but without the amount spent on stuff that is not a direct cost of buying the property.

But how you calculate your percentage shares of the flat could be the least of your worries. If your boyfriend takes out a mortgage in his sole name, the lender will insist that the flat is bought in his name so only his name will appear on the title register held by the Land Registry (or, in the past, on the title deeds).

A mortgage cannot be arranged where anyone named on the title register (or deeds) is not also a mortgage borrower. So even if your boyfriend will take full responsibility for paying the mortgage, if you want to be listed on the title register as a joint owner of the flat – and so have your £200,000 contribution to it recognised – you need to be named on a joint mortgage as well.

As well as making sure that you are registered as the joint owner of the flat and on the joint mortgage, you and your boyfriend should get a solicitor to draw up a deed of trust. This should set out your percentage shares in the property and cover what will happen if you decide to split up and either sell the flat, or you decide to buy your boyfriend out or vice versa.