The 8 steps
- Check you need to file. Register for Self Assessment by 5 October after the tax year if rental income is over £2,500 after expenses or £10,000 before expenses, or if HMRC asks you to file.
- Gather your records. Collect rent received, every expense with receipts, mortgage interest statements and your UTR.
- Choose expenses or the £1,000 allowance. Compare your actual costs with the £1,000 property allowance. Claim whichever gives the lower tax.
- Enter income in box 20. Put total rent and other property income in box 20, before agent fees.
- Sort costs into boxes 24 to 29 and 36. Running costs go in boxes 24 to 29 by type; replacing furniture and appliances goes in box 36.
- Enter mortgage interest in box 44. Put 100% of residential finance costs in box 44. HMRC turns it into a 20% tax credit.
- Check profit, losses and carry-forwards. Use HMRC's working sheet for box 38 (profit) or 41 (loss); use boxes 39, 43 and 45 for amounts from other years.
- Submit and pay by 31 January. File online and pay any tax due, plus your first payment on account if it applies.
What goes in each box
| Box | HMRC title | What to enter |
|---|---|---|
| 20 | Total rents and other income from property | Gross rent from all UK lets, before agent fees |
| 20.1 | Property income allowance | Up to £1,000, if you claim it instead of expenses |
| 20.2 | Traditional accounting | Tick only if you don't use the cash basis (required above £150,000 income) |
| 21 | Tax taken off | Non-resident landlords only |
| 22 / 23 | Lease premiums / reverse premiums | Rare for ordinary buy-to-let |
| 24 | Rent, rates, insurance, ground rents etc | Insurance, ground rent, service charges, council tax and bills you pay |
| 25 | Property repairs and maintenance | Like-for-like repairs and redecoration, not improvements |
| 26 | Non-residential property finance costs | Interest on commercial property only |
| 27 | Legal, management and other professional fees | Letting agent, accountant, eviction and short-lease legal costs |
| 28 | Costs of services provided, including wages | Cleaning, gardening, other services you pay for |
| 29 | Other allowable property expenses | Safety certificates, travel, phone, stationery, advertising |
| 30 to 35 | Private use, balancing charges, capital allowances | Mostly for commercial or mixed property |
| 36 | Costs of replacing domestic items | Like-for-like furniture, appliances, carpets in residential lets |
| 37 | Rent a Room exempt amount | If you claim Rent a Room relief for a lodger |
| 38 / 41 | Profit / loss | From HMRC's working sheet in the notes |
| 39 | Losses brought forward used | Earlier property losses set against this year's profit |
| 43 | Loss to carry forward | Unused losses for next year |
| 44 | Residential property finance costs | 100% of mortgage interest and finance costs |
| 45 | Unused residential finance costs brought forward | Interest that couldn't get the credit in earlier years |
Box titles are from HMRC's notes for the 2025/26 UK property pages. Online, the same items appear as questions rather than numbered boxes, in the same order.
Worked example
Sam lets one flat for £1,200 a month (£14,400 a year). In 2025/26 Sam paid £650 for insurance and ground rent, £900 of repairs, £1,440 to a letting agent, £300 for a gas safety check, EICR share and phone, £400 to replace a broken washing machine, and £5,000 of mortgage interest.
| 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 |
Total expenses are £3,690, so profit is £10,710. The £5,000 of interest gives a credit of £1,000. If Sam is a higher-rate taxpayer, the tax is £4,284 − £1,000 = £3,284. Check it in the helper.
Expenses or the £1,000 property allowance?
You can deduct your actual expenses or claim the £1,000 property allowance, not both. The allowance only beats real expenses if your costs are under £1,000 and you have no mortgage, because claiming it also means no mortgage interest credit. If your total property income is £1,000 or less, you may not need to report it at all.
Common mistakes
- Putting mortgage interest in box 24 or 29 as well as, or instead of, box 44.
- Entering rent after the agent's fee, then claiming the fee again in box 27, or claiming it not at all.
- Claiming the full cost of improvements, such as a new extension or upgrading to a better kitchen. These are capital costs, relevant when you sell.
- Claiming the first purchase of furniture in box 36. Only replacements qualify.
- Including mortgage capital repayments. Only the interest counts.
- Joint owners each entering the full figures. Each enters their own share, usually 50% for married couples.
- Claiming the £1,000 allowance and expenses together. It's one or the other.
After you file
If your bill is over £1,000 and less than 80% of your tax is collected through PAYE, you'll also make payments on account: half of this year's bill on 31 January and again on 31 July. Plan them with our payments on account planner. If your qualifying income was over £50,000 in 2024/25, you're already in Making Tax Digital from April 2026 and send quarterly updates as well.
Key dates
| Date | What |
|---|---|
| 5 October 2026 | Register for Self Assessment if you're new (for 2025/26) |
| 31 October 2026 | Paper return deadline |
| 30 December 2026 | File online by this date to pay through your tax code (if eligible) |
| 31 January 2027 | Online return and payment deadline |
| 31 July 2027 | Second payment on account |
Missing 31 January costs £100 straight away, even if you owe no tax. See the full landlord tax calendar.
Frequently asked questions
Do I need to fill in the SA105 for one rental property?
Yes, if your rental income is over £1,000 and you're in Self Assessment. One set of UK property pages covers all your UK lets.
Where do I put letting agent fees on my tax return?
Box 27, legal, management and other professional fees. Report rent in box 20 before the agent's fees were taken off.
Can I claim mortgage interest as an expense on my tax return?
Not for residential lets. Enter it in box 44 and HMRC gives a basic-rate credit instead: 20% up to 2026/27 and 24% from 2027/28.
What is box 36 on the SA105?
Costs of replacing domestic items, such as furniture, appliances and carpets, in residential lets. Only replacements count, not the first purchase.
Sources
- HMRC: UK property notes (SA105 Notes 2025)
- GOV.UK: Self Assessment deadlines
- 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: Payments on account
Sources last checked 10 November 2026. See all our sources and how we keep pages up to date.