Jointly owned property: why 50/50 isn't always the answer

Who pays the tax on a jointly owned rental?

The starting point is simple. Each owner reports their share of the rental profit on their own Self Assessment tax return. There's no separate joint return, and no single bill that gets split afterwards. You each declare your slice of the rental income tax and pay tax on it at your own rate.

What's far less simple is working out what that slice actually is. The answer turns on two things: whether you're married or in a civil partnership, and the concept of beneficial ownership, which is who's genuinely entitled to the income, not just whose name is on the deeds.

Married couples and civil partners: 50/50 by default

Here's the part that catches people out. If you're married or in a civil partnership, living together, and you own a rental property jointly, HMRC taxes the income 50/50 by default. That's set out in section 836 of the Income Tax Act 2007.

It applies even when your actual ownership shares are nothing like equal. You could own 90% of the property and your spouse 10%, and HMRC will still tax the rental profit half each unless you tell them otherwise. For many couples that's fine. For some it's expensive, and for some it's the wrong way round entirely.

To be taxed on your real shares instead, you make a Form 17 declaration. More on that below.

Unmarried co-owners: your actual shares

If you own a property jointly with someone who isn't your spouse or civil partner, the 50/50 default doesn't apply to you. Your share of the profit normally follows the share of the property you actually own. Two friends who own 60/40 are taxed 60/40.

You can agree a different split of the profits if you want to, but you need to be able to evidence it, and the share you declare should stay consistent year to year unless your circumstances genuinely change.

What happens if one of you owned the property before marriage?

This is the scenario that trips couples up most, so let's work it through properly.

Priya bought a flat years before she met Daniel. It's in her sole name. They marry, buy a home together, and decide to keep the flat and let it out. The rent comes in, and they assume that now they're married they'll naturally split the rental income 50/50.

They won't, and this is the bit worth understanding. The 50/50 default only applies to property the couple owns *jointly*. Priya's flat is hers alone, legally and beneficially. So if they do nothing, all of the rental profit is Priya's, and she declares 100% of it on her own Self Assessment. Getting married changed nothing on its own.

If Priya is the higher earner and Daniel has unused allowances or a lower tax band, leaving everything on Priya's return may mean paying more tax than they need to. To bring Daniel in, Priya would have to transfer him a genuine beneficial interest in the flat, putting it into joint names or a declaration of trust. The moment they own it jointly, the 50/50 default switches on. And if they want something other than 50/50, that's where Form 17 comes back in.

When does Form 17 apply?

Form 17 is the declaration married couples and civil partners use to be taxed on their actual beneficial ownership shares rather than the 50/50 default. If you own a jointly held property 75/25 and that reflects the real beneficial ownership, Form 17 lets you be taxed 75/25.

Two conditions matter. First, your beneficial interests in the property and in the income from it have to correspond. You can't own 75% of the property but claim 90% of the income; the form only works where the income split matches the ownership split. Second, you need to be able to back it up. HMRC can ask for evidence, such as a declaration of trust, showing the beneficial ownership is really what you've declared.

Form 17 also only works for property held in unequal shares. If you genuinely own it 50/50, there's nothing to elect, because the default already matches reality.

Where joint ownership goes wrong

The mistakes here tend to be quiet ones. They don't announce themselves until HMRC asks a question, often years later.

The most common is declaring a split you can't support. A couple decides the higher earner should report less, so they put 30% on one return and 70% on the other, without ever changing the beneficial ownership or filing Form 17. On paper it saves tax. In reality it's a figure HMRC can unpick, because the income split doesn't match the ownership and there's no valid declaration behind it.

Others file Form 17 incorrectly, or assume it backdates. It doesn't. A declaration takes effect from the date it's made, not the start of the tax year, and it has to reach HMRC within 60 days of being signed to be valid. Miss that window and you're back on the 50/50 default for that period.

The frustrating part is that the right answer is often more tax-efficient than the wrong one. Getting the ownership and the paperwork lined up properly can legitimately put more income in the hands of the lower earner. It just has to be real, and it has to be documented.

Getting the split right

Jointly owned property rewards getting the structure right before the rent starts flowing, not patching it afterwards. Decide who genuinely owns what, make sure the income follows the ownership, file Form 17 where it helps, and keep the evidence. Each of you then reports your share on your own return, the same way you'd handle the rest of your property pages on the SA105.