A landlord client files the tax return late: the £100, £900 and 5% penalties worked out at £2,000 and £10,000 of tax

A landlord who owns one or two rentals often files a Self Assessment return only because the rent crosses a line. When the return slips, the penalties do not scale with the rent: part of them is a fixed sum. That matters most for the client with a small tax bill, who may not realise the penalty can be several times the tax. A letting agent that sends a yearly income statement is often the first to notice the return has not been filed.

The dates, as GOV.UK gives them

For the 2025 to 2026 tax year (6 April 2025 to 5 April 2026), GOV.UK's deadlines page gives these dates:

The penalty steps

GOV.UK's penalties page lists these for a late return:

• £100 straight away once the return is late.
• After 3 months, £10 a day, up to a maximum of £900.
• After 6 months, a further 5% of the tax due or £300, whichever is greater.
• After 12 months, another 5% of the tax due or £300, whichever is greater.

For tax paid late, the page gives 5% of the unpaid tax at 30 days, at 6 months and at 12 months, plus interest on what is owed. It does not state the interest rate, so the sums below leave interest out. Penalties are due within 30 days of the penalty notice.

Two clients, both 7 months late

Take two landlord clients who file and pay 7 months after 31 January 2027, that is in late August 2027. By then the £10 a day has reached its £900 cap and the 6-month steps have applied, but not the 12-month ones.

The arithmetic: Client A is 1,500 + 1,000 = 2,500, and 2,500 / 10,000 = 0.25. Client B is 1,300 + 200 = 1,500, and 1,500 / 2,000 = 0.75. The payment is where the client with the small bill is protected, because it is a percentage. The return penalties are where they are exposed, because £100, £900 and the £300 minimum do not shrink.

If client B had filed on time and only paid 7 months late, the penalties would have been £200, which is 10% of the tax. So filing the return matters more than the cheque.

What we did not read

The pages we read describe the penalties in this form. We did not read how the points-based late submission system for Making Tax Digital applies to landlords, and we did not read HMRC's reasonable excuse guidance or the appeal route. Our Making Tax Digital guide covers the quarterly side. Check the landlord's own position with HMRC or an accountant before telling them a penalty can be waived.

What an agent can do before the date

The agent cannot file a client's return unless it is authorised, and should not give tax advice. It can send the yearly statement of rent and costs early, and name the 31 January date in the cover note. Items that reduce the profit on the return, such as the £1,000 property allowance or the mortgage interest tax reduction, are worth mentioning so the client asks their accountant about them in time.

Where Overlyft fits

Overlyft can set up AI staff who join your lettings team and take the job of preparing each landlord's year-end statement and a dated reminder for 5 October, 30 December and 31 January. A person in your office approves every statement and every message before it goes out.

This is general information for England, not tax or legal advice.