Self Assessment is HMRC's system for collecting tax from people with income that is not taxed at source through PAYE. Rental income falls outside PAYE, so landlords must self-report. The system is straightforward once you understand its structure: the main SA100 return is supplemented by SA105 (UK property income), SA109 (non-UK residence if applicable), and potentially SA108 (capital gains on disposal of property).
The 2025–26 tax year runs from 6 April 2025 to 5 April 2026. Paper returns for this year were due 31 October 2026. Online returns are due 31 January 2027. Any tax owed must also be paid by 31 January 2027, with a second payment on account potentially due 31 July 2027.
Do landlords need to register for Self Assessment?
You must register and file if any of the following apply:
- Your gross rental income (before expenses) exceeds £1,000 in the tax year, the property allowance threshold
- You have made a loss on rental income that you want to carry forward or offset against future profits
- You are a non-resident landlord receiving UK rental income (you must also apply for gross receipt approval through the Non-Resident Landlord scheme)
- HMRC has sent you a notice to file a return, you must file even if you think no tax is due
- You have other income that requires a return (self-employment, high income child benefit charge, foreign income) and you also have rental income to declare
How to register for Self Assessment
New landlords must notify HMRC by 5 October following the end of the tax year in which they first received rental income:
- Register online at HMRC's 'Register for Self Assessment' service, you will need a Government Gateway account
- HMRC will issue a Unique Taxpayer Reference (UTR) by post within 10 working days. Keep this, you need it to file every year
- If you already file a Self Assessment return (e.g. for self-employment), simply add the SA105 property pages to your existing return
- Late registration: if you miss the 5 October deadline, register immediately. HMRC may charge a failure-to-notify penalty, but early voluntary disclosure usually results in no penalty
- Non-resident landlords: also register with the Non-Resident Landlord scheme (NRLS) at HMRC. If approved, your letting agent or tenant does not deduct basic rate tax from rent before paying you
Completing the SA105 property income pages
The SA105 has two main sections: furnished holiday lettings (FHL) and UK property income. For most buy-to-let landlords, only the UK property section applies:
- Box 20: total rents and other receipts, enter gross rent received in the tax year, including any rent paid late or in advance
- Box 24: tax taken off income, if basic rate tax was deducted by a tenant or agent (non-resident landlords only), enter it here
- Boxes 27–38: allowable expenses, enter each deductible expense in the relevant box
- Box 39: private use adjustment, if any part of a property is used privately, reduce the expense claim proportionally
- Box 43: adjusted profit or loss, HMRC calculates taxable profit after all deductions
- Box 45: residential finance costs, enter the total mortgage interest and other qualifying finance costs. These are not deducted here; instead a 20% basic rate credit is calculated on your tax computation (the Section 24 restriction)
- Box 46: unused finance costs brought forward, if prior year finance cost relief was unused, enter the carried-forward amount here
Section 24, reporting mortgage interest on Self Assessment
Section 24 changed how mortgage interest is reported since April 2020:
- Do not deduct mortgage interest in the expense boxes of SA105. It is no longer a deductible expense
- Enter total finance costs (mortgage interest, loan arrangement fees, alternative finance payments) in Box 45 of SA105
- HMRC's tax calculation will add back these costs to your income and then apply a 20% basic rate tax credit
- For basic rate (20%) taxpayers, the net effect is neutral. For higher-rate (40%) and additional-rate (45%) taxpayers, the restriction costs additional tax
- Unused finance costs: if the 20% credit exceeds your tax liability, unused costs can be carried forward to the next year, report in Box 46
Filing deadlines and payment dates
The key dates for the 2025–26 tax return:
- 5 October 2026: deadline to register for Self Assessment if this is your first year
- 31 October 2026: paper return filing deadline for 2025–26
- 31 January 2027: online return filing deadline and payment deadline for any tax owed
- 31 July 2027: second payment on account deadline (if applicable)
- Late filing penalty: £100 automatic penalty if you miss the 31 January deadline; further daily penalties (£10/day up to 90 days) from 3 months late
- Late payment interest: HMRC charges interest on unpaid tax from 1 February at the Bank of England base rate plus 2.5%
Record-keeping requirements
HMRC requires landlords to keep records for at least 22 months after the end of the tax year to which they relate:
- Rent receipts: bank statements or rent accounts showing all rental receipts
- Expense receipts: invoices for repairs, agent fees, insurance, professional fees
- Mortgage statements: year-end statements showing interest paid
- Tenancy agreements: retain throughout the tenancy and for at least 6 years after end
- HMRC Making Tax Digital (MTD) 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
Frequently asked questions
What is the deadline for landlords to register for Self Assessment?+
You must register by 5 October following the end of the tax year in which you first received rental income. For the 2025–26 tax year (ending 5 April 2026), the registration deadline is 5 October 2026. If you miss this, register immediately, HMRC may waive the failure-to-notify penalty if you come forward voluntarily and there is a reasonable excuse.
Do I need to file a Self Assessment if my rental income is under £1,000?+
If your gross rental income (before any expenses) is £1,000 or less in the tax year, you can use the Property Income Allowance and are not required to register for Self Assessment or pay any tax on rental income. If HMRC has already issued you a notice to file, you must still file the return even if no tax is due.
Where do I put mortgage interest on my Self Assessment return?+
Mortgage interest is reported in Box 45 of the SA105 supplementary pages, not in the expense boxes. Due to Section 24, mortgage interest is no longer deducted as an expense. Instead, HMRC applies a 20% basic rate tax credit based on the figure in Box 45. For basic rate taxpayers the effect is neutral; higher-rate taxpayers pay more tax than before 2017.
Can I file a landlord Self Assessment return myself or do I need an accountant?+
You can file yourself using HMRC's free online Self Assessment system. Most landlords with straightforward portfolios (a few residential lets, no FHLs or overseas property) can complete the SA100 and SA105 without professional help. An accountant adds most value when you have complex situations: multiple properties, Section 24 exposures, losses to carry forward, potential incorporation, or capital gains from sales.