What is Self Assessment?

Self Assessment

HMRC’s system for reporting untaxed income, including rental profit, and paying the tax due. Most landlords must register for Self Assessment and file a return by 31 January after the tax year, paying any tax by the same date. Making Tax Digital is progressively replacing the single annual return with digital quarterly updates for landlords above the income thresholds.

Reviewed by Erdem VolkanLast reviewed 16 September 2026How we check facts

Why it matters

What Self Assessment means for a landlord

A new landlord must register for Self Assessment by 5 October following the tax year they started letting, miss it and penalties follow even if little tax is due. The 31 January deadline covers both filing and payment, and larger bills also trigger payments on account. As MTD for Income Tax rolls out, the record-keeping burden shifts from a once-a-year scramble to ongoing digital bookkeeping, which is exactly the gap purpose-built landlord software is designed to close.

Worked example

How it plays out

Lucy starts letting a flat in May 2025, in the 2025 to 2026 tax year. She registers for Self Assessment by 5 October 2026, files her return online, and pays the tax by 31 January 2027.

An illustrative example. Names, places and figures are made up.

Common mistakes

Where landlords go wrong

01Missing the 5 October registration deadline in your first year.
02Forgetting payments on account for the following year.
03Leaving the records until January.

What to do

A short checklist

Register as soon as you start letting.
Diary 31 January and 31 July.
Update your records every month.

Sources

GOV.UK, Self Assessment

Checked against these sources on 16 September 2026. A guide to the rules in England, not legal advice: for a dispute or a possession claim, speak to a solicitor.