Apportioning Rental Expenses: Claiming the Right Share (2026/27)
Last updated 24 June 2026 · 8 min read · By the LandlordTaxAi Editorial Team
The short answer
When an expense is only partly for your rental business, you can deduct a fair, reasonable share — not the whole cost. This applies to costs split between private and rental use, a property let for only part of the year, or a room let within your home. The calculator above works out the deductible portion.
Plenty of landlord costs aren’t 100% business: a phone you also use personally, a property you lived in for part of the year, a car used for both. HMRC’s rule is that you can claim the part that’s wholly and exclusively for the lettings — and the skill is apportioning it fairly and defensibly.
The calculator above turns a mixed cost into the deductible share. This guide explains the main apportionment situations for 2026/27. For what’s deductible in the first place, see allowable expenses for landlords.
Free calculator · no sign-up
Rental Expense Apportionment Calculator
Work out the deductible business share of mixed or part-year costs for 2026/27.
Result
- Taxable profit (rent − expenses)
- £11,200
- Income Tax at 20%
- £2,240
- Less mortgage interest credit (20%)
- − £1,000
- Tax due on this property
- £1,240
- Income after tax
- £9,960
Claim only the business portion on a reasonable basis. Estimate only, not personalised advice.
The wholly-and-exclusively rule (and its exception)
An expense is only deductible if it’s incurred wholly and exclusively for the property business. Strictly, a cost with a private element fails that test — but there’s an important exception: where a definite, identifiable part of the expense is for the business, you can deduct that part.
So a cost that’s 60% business and 40% private isn’t disallowed entirely — you claim the 60%, as long as you can justify the split.
The key is a reasonable basis for the split — by time, by floor area, by mileage, or by usage — and keeping the workings so you can show HMRC how you arrived at the figure.
Common apportionment situations
Most apportionment falls into a handful of recurring scenarios. The right method depends on what’s being shared.
| Situation | Apportion by |
|---|---|
| Phone / broadband used privately and for lettings | Business-use percentage |
| Property let for only part of the tax year | Months (or days) let vs total |
| A room let within your own home | Floor area and/or time |
| Car used for property trips and privately | Business mileage (or use the mileage rate) |
| A cost covering several properties | Split across the properties it relates to |
Don’t claim a full year’s costs on a property you only let for part of the year — apportion running costs to the period it was available to let. The same applies to a property that was your home before you let it.
How to apportion fairly
Whatever the cost, the method should reflect how much of it genuinely served the lettings business.
Claim the right share, every time
LandlordTaxAi apportions mixed costs across private use, part-year lets and multiple properties automatically — so you claim exactly what you’re entitled to and no more.
See how it worksA worked example
Sara lets a property from 6 July 2026 (having lived in it before). Annual buildings insurance is £360 and she uses her phone 30% for lettings (£200 annual bill).
| Insurance — let 9 of 12 months | £360 × 9/12 = £270 |
| Phone — 30% business use | £200 × 30% = £60 |
| Total apportioned deduction | £330 |
| Disallowed private portion | £230 |
Sara claims £330 — the genuine business share — not the full £560. Apportioning correctly is both compliant and still worth real money.
Frequently asked questions
Can I claim an expense that’s partly private?
Yes, the business part. Where a definite portion of a cost is wholly and exclusively for the lettings, you deduct that share — not the whole amount.
How do I apportion a cost?
Use a reasonable basis — time, floor area, mileage or usage — that reflects how much of the cost served the rental, and keep your workings.
What if I only let the property part of the year?
Apportion running costs to the period it was available to let. Don’t claim a full year on a property let for only part of it.
How do I split costs across several properties?
Allocate the cost across the properties it relates to on a fair basis, so each property carries its share.
Can I claim part of my home costs?
If you run lettings from home, yes — see the use-of-home rules. If you let a room, apportion by floor area and time.
Does HMRC accept apportionment?
Yes, provided the split is reasonable and supported by your records. Keep notes of how you calculated each business percentage.
Written and reviewed by the LandlordTaxAi Editorial Team. Our guides are reviewed against current HMRC guidance and updated when the rules change. Operated by LandlordTaxAi, United Kingdom. Follow us on LinkedIn.
Last reviewed: 24 June 2026 · Researched against primary UK sources for the 2026/27 tax year: https://www.gov.uk/guidance/income-tax-when-you-rent-out-a-property-working-out-your-rental-income; https://www.litrg.org.uk/savings-property/property-income/working-out-property-income. This article is informational only and does not constitute tax advice. Check the latest details on GOV.UK or with a qualified accountant.