Who must register for Self Assessment?
Every landlord whose gross rental income exceeds £1,000 in a tax year must register for Self Assessment. Register by 5 October following the end of the relevant tax year, for 2025–26, that is 5 October 2026.
The SA105 property income pages
- Box 20: gross rents and other receipts
- Boxes 27–38: allowable expenses (repairs, agent fees, insurance, professional fees)
- Box 45: residential finance costs (mortgage interest, entered separately under Section 24)
- Box 44: loss to carry forward (if expenses exceed income)
Section 24, how to report mortgage interest
Mortgage interest is NOT deducted as an expense. Enter total finance costs in Box 45. HMRC applies a 20% basic rate tax credit. Higher-rate taxpayers receive less relief than before 2017.
Key filing deadlines for 2025–26
| Deadline | Action |
|---|---|
| 5 October 2026 | Register for Self Assessment (new landlords) |
| 31 October 2026 | Paper return deadline |
| 31 January 2027 | Online return deadline and tax payment |
| 31 July 2027 | Second payment on account (if applicable) |
An automatic £100 penalty applies for missing the 31 January deadline. After 3 months, £10 per day penalties accrue. After 6 and 12 months, 5% surcharges on unpaid tax are added.
Record-keeping
- Rent receipts (bank statements or rent accounts)
- Expense invoices and receipts
- Year-end mortgage interest statements
- Tenancy agreements
- Keep records for at least 22 months after the end of the relevant tax year
HMRC's Making Tax Digital for income tax is expected to apply to landlords with gross income above £30,000 from April 2026, requiring quarterly digital submissions via compatible software.