Landlord tax return helper: SA105 box by box
Type in your rent and costs for the tax year. The helper sorts them into HMRC's boxes on the UK property pages and works out your profit and mortgage interest credit.
Key facts
- The 2025/26 return is due online by 31 January 2027.
- Rent goes in box 20; running costs in boxes 24 to 29; replacing furniture and appliances in box 36.
- Mortgage interest goes in box 44, not in the expense boxes. HMRC gives a 20% tax credit on it.
- If your costs are under £1,000 and you have no mortgage, the £1,000 property allowance (box 20.1) may be better.
How the helper sorts your figures
The boxes follow HMRC's notes for the UK property pages (SA105). Rent and any other property income go in box 20. Running costs go in boxes 24 to 29, depending on the type of cost. The cost of replacing furniture, appliances and furnishings in a residential let goes in box 36. Your profit, box 38, is income minus those costs.
Residential mortgage interest is never an expense. It goes in box 44, and HMRC turns it into a tax credit of 20% of the lowest of: your finance costs (plus any brought forward), your property profit after losses, and your income above the Personal Allowance. The helper checks the first two limits.
Worked example
A landlord receives £14,400 rent. Costs are £650 for insurance and ground rent, £900 of repairs, £1,440 agent fees, £300 of other costs and £400 to replace a washing machine. Mortgage interest is £5,000.
| Box | What | Amount |
|---|---|---|
| 20 | Total rents and other income from property | £14,400 |
| 24 | Rent, rates, insurance, ground rents etc | £650 |
| 25 | Property repairs and maintenance | £900 |
| 27 | Legal, management and other professional fees | £1,440 |
| 29 | Other allowable property expenses | £300 |
| 36 | Costs of replacing domestic items | £400 |
| 38 | Profit (from HMRC's working sheet) | £10,710 |
| 44 | Residential property finance costs | £5,000 |
Profit is £10,710. The mortgage interest credit is 20% of £5,000 = £1,000. A higher-rate taxpayer pays £10,710 × 40% − £1,000 = £3,284; a basic-rate taxpayer £1,142. These are the defaults above, so you can check the helper against them.
Before you start
You need your rent and expense records for 6 April to 5 April, your Unique Taxpayer Reference (UTR) and your mortgage statements showing the interest charged. Our free landlord spreadsheet uses the same categories as these boxes. For the full walkthrough, read how to fill in the SA105.
What this helper doesn't cover
Lease premiums (box 22), reverse premiums (box 23), capital allowances (boxes 30 to 35), Rent a Room (box 37), non-resident landlord tax (box 21) and furnished holiday lets before April 2025. Joint owners should enter only their own share of each figure. If any of these apply, read HMRC's SA105 notes or use an accountant.
Frequently asked questions
Where does mortgage interest go on the SA105?
Box 44, residential property finance costs. Enter 100% of the interest. Don't include it in boxes 24 to 29.
Which box is for replacing a fridge or sofa in a rental?
Box 36, costs of replacing domestic items, for like-for-like replacements in residential lets. The first purchase of an item isn't allowable.
Do I need to fill in the SA105 if my rent is under £1,000?
Usually not. If your total property income is £1,000 or less you can use the property allowance and may not need to report it, unless you're already in Self Assessment for other reasons.
Does the helper send my figures anywhere?
No. Everything is calculated in your browser.
Sources
- HMRC: UK property notes (SA105 Notes 2025)
- GOV.UK: Tax relief for residential landlords, how it's worked out
- GOV.UK: Tax-free allowances on property and trading income
- GOV.UK: Work out your rental income when you let property
- GOV.UK: Self Assessment deadlines
Sources last checked 10 November 2026. See all our sources and how we keep pages up to date.