Scope: applies UK-wide; Scotland sets its own income tax rates and bands. 2026/27 tax year.
A couple owns a rental 90/10. One is a higher-rate taxpayer, the other has unused personal allowance. They assume the income follows the deeds. For married couples and civil partners it does not, and the default costs them money every year until they fix it.
The default
Income from property held jointly by spouses or civil partners living together is taxed 50/50, regardless of the actual beneficial ownership. Own it 90/10 and you are still taxed 45/45 unless you act.
Unmarried joint owners are different. They are taxed on their actual beneficial shares by default, and there is no Form 17 — it applies only to spouses and civil partners.
Changing it takes two documents, in order
1. A declaration of trust
First you must actually own it unequally in beneficial terms. A declaration of trust (or deed of trust) records the beneficial split. Without it there is nothing to declare, and Form 17 cannot manufacture a split that does not exist.
This is legal work, not tax work. Get it drafted properly, especially where there is a mortgage — changing beneficial shares where debt is assumed can have its own SDLT or LTT consequences.
2. Form 17
Then you tell HMRC, on Form 17, that you want to be taxed on actual shares rather than 50/50. Points that catch people:
- It must reach HMRC within 60 days of being signed. Late, and it is invalid — you start again.
- Both must sign.
- Evidence of the beneficial split must go with it.
- It takes effect from the date of the declaration, not the start of the tax year. It is not retrospective, so a late form means a year taxed 50/50.
- It applies only to income. It does not change the CGT position, which follows beneficial ownership regardless.
It cannot be 100/0
The rule needs joint ownership, so both must retain a beneficial interest. A 99/1 split works; 100/0 is not joint ownership and Form 17 does not apply — at which point you are talking about a transfer, not a declaration.
It sticks until circumstances change
A valid Form 17 runs until the beneficial split changes, you separate or divorce, or one of you dies. You do not re-file annually. But if you later change the shares you need a new declaration and a new Form 17.
Why it is worth doing
Shifting income to the lower earner uses their personal allowance and basic rate band. Where section 24 has inflated one spouse’s declared income, moving rent to the other can also keep them under the higher-rate threshold, out of the personal allowance taper, or clear of the High Income Child Benefit Charge — effects worth more than the headline rate difference.
And it changes your MTD position
Your share of the gross rents counts towards your qualifying income for Making Tax Digital. Two spouses at 50/50 on £80,000 of rent have £40,000 each. Move to 90/10 and one has £72,000 — over the £50,000 threshold, and now mandated.
Ownership does not change the duties. Check what applies to the property — five questions, no signup.
Information tool, not tax or legal advice. A declaration of trust is legal work; take advice.