Rental income has been back in the headlines this week, and it is a useful prompt for every UK landlord to check one thing: is your rental income being declared to HMRC correctly? It is one of the most common areas where well-meaning landlords slip up, not through dishonesty, but because the rules changed significantly in recent years and the way HMRC detects undeclared rent has changed even faster.
This guide walks through exactly how to declare rental income in 2026: who needs to report, how to register, what is taxable, the Section 24 trap, the expenses landlords miss, and how to put things right if you are behind. For the wider picture on what you must report, see our companion guide to landlord tax returns and rental income.
Do You Actually Need to Declare Your Rental Income?
Most landlords do. The thresholds that decide it are:
- Under £1,000 gross rental income a year: covered by the property allowance. You usually do not need to report it.
- Rental profit of £2,500 or more: you must report through Self Assessment.
- Profit between £1,000 and £2,500: contact HMRC; they may collect the tax through an adjustment to your tax code rather than a full return.
A point that catches people out: this applies even to "accidental" landlords. If you moved in with a partner and kept your old flat, inherited a property and let it, or rent out a single room beyond the £7,500 Rent-a-Room limit, the income is still taxable and reportable.
Step One: Register to Declare Rental Income
Before you can declare anything, you need to be registered for Self Assessment as a landlord. You do this with HMRC's form SA1 (the registration route for non-self-employed income such as property).
The deadline matters: you must register by 5 October following the end of the tax year in which you first received rental income. So if you started letting a property during the 2025/26 tax year, you needed to register by 5 October 2026. Register late and you can face penalties even before a single return is filed.
Once registered, HMRC issues your Unique Taxpayer Reference (UTR), which you use to file. First-time landlords are exactly the group who most often miss this step, because they assume reporting only starts when they get round to the return itself.
Step Two: Know What Counts as Rental Income
Rental income is more than the monthly rent. It includes rent received, any non-refundable deposits you keep, charges to tenants for services where you pay the cost and recharge them, and income from short lets through platforms such as Airbnb. If you let a room in your own home, the first £7,500 a year is tax-free under Rent-a-Room, but anything above that is reportable.
Step Three: Claim the Right Expenses (and Avoid the Section 24 Trap)
You are taxed on your profit, not your rent, so allowable expenses matter. Fully deductible costs include letting agent fees, landlord insurance, ground rent and service charges, accountancy fees, advertising for tenants, and genuine repairs and maintenance.
The single biggest trap is mortgage interest. Since the Section 24 rules fully took effect, you can no longer deduct mortgage interest from your rental profit. Instead you receive a basic-rate (20%) tax credit on your finance costs. For a higher-rate taxpayer this is a meaningful difference, and many landlords still calculate it the old way, producing an incorrect return that either overstates relief or understates tax.
Expenses landlords most often forget
- Accountancy fees for preparing the rental accounts.
- Mileage or travel to inspect the property and meet tradespeople.
- Replacement of domestic items relief (sofas, beds, white goods in a furnished let).
- Phone and admin costs proportionate to running the let.
- Council tax and utilities you pay during void periods.
Step Four: File and Pay on Time
Rental income is declared on the SA105 property pages of your Self Assessment return (SA106 for foreign property). The key dates for a tax year ending 5 April are:
- 5 October, register for Self Assessment if it is your first year.
- 31 January, file your online return and pay the tax due.
From 6 April 2026, Making Tax Digital for Income Tax also begins for landlords with property (and self-employment) income above £50,000, who must keep digital records and send quarterly updates. Those between £30,000 and £50,000 follow from April 2027.
How HMRC Knows About Your Rental Income
This is the part landlords underestimate. HMRC no longer relies on you to volunteer the information. It receives and cross-references data from:
- Letting and managing agents.
- Tenancy deposit protection schemes.
- The Land Registry (who owns what).
- Mortgage lenders (buy-to-let mortgages are visible).
- Online platforms such as Airbnb, which now share host earnings data.
When that data does not match a tax return, it flags. Undeclared rental income that might have gone unnoticed a decade ago is now far more likely to surface, which is exactly why a story about rental income trending in the news is a good moment to make sure yours is in order.
Already Behind? Use the Let Property Campaign
If you have not declared rental income for one or more past years, the worst thing to do is nothing. HMRC's Let Property Campaign is a voluntary disclosure route designed for exactly this situation. Coming forward voluntarily almost always results in lower penalties than waiting for HMRC to open an enquiry, and you can normally still claim the expenses and reliefs you were entitled to for those years.
A landlord came to us having let a flat for three years without realising the rent needed declaring, they assumed the mortgage "cancelled out" the income. It did not, because of Section 24.
We brought all three years up to date through the Let Property Campaign, claimed expenses they had never recorded, and negotiated the penalty position because the disclosure was voluntary. The final bill was a fraction of what an HMRC-opened investigation would have cost, and they now have a clean, accurate baseline going forward.
The Mistakes That Cost Landlords Most
- Not registering on time, missing the 5 October deadline.
- Treating mortgage interest as a normal expense instead of the 20% Section 24 credit.
- Claiming capital improvements as repairs (or missing the CGT benefit of capital costs at sale).
- Forgetting allowable expenses, agent fees, insurance, accountancy and travel.
- Assuming small or occasional rent doesn't count, it does, above the £1,000 allowance.
Frequently Asked Questions
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