Renting to Family Members Below Market Rent: Tax Implications 2026/27

Why HMRC treats family lettings differently

It's common for homeowners to let a property — perhaps an inherited house, or a second property — to an adult child, parent, or other family member at a reduced rent, often to help them out financially. HMRC recognises this is a genuine and common arrangement, but applies specific rules (sometimes referred to as the "uncommercial letting" rules) to prevent below-market family arrangements from being used to generate artificial tax losses that offset other income.

The core restriction: expenses capped at rent received

If you let a property to a family member at a rent significantly below the market rate, HMRC generally restricts your allowable expense deductions to the amount of rent actually received — you can't deduct more in expenses than you earned in rent, even if your genuine allowable costs (insurance, maintenance, a share of mortgage interest credit) would normally exceed that. In effect, this means:

• You can't create a loss on the below-market letting to offset against other income
• Any excess unused expenses may, in some circumstances, be carried forward to offset against rental income from the same property in future years — but only if that future income comes from the same source
• This restriction only applies to the below-market element — if you also let other properties commercially, those remain unaffected

Worked example: below-market family letting

Situation: A homeowner lets a second property to their adult daughter for £400/month (£4,800/year), while the genuine market rent for a similar property in the area is £900/month (£10,800/year) — a clear, substantial discount reflecting the family relationship rather than a commercial rate.

Allowable expenses for the year: Insurance £350, maintenance £600, letting-related costs £150 = £1,100 total.

Tax treatment: Since expenses (£1,100) are below the rent received (£4,800), there's no restriction issue here — the full £1,100 is deductible, leaving taxable profit of £3,700. The restriction would only bite if expenses had exceeded the £4,800 rent received, in which case the excess couldn't be used to create a loss.

Worked example: where the restriction actually matters

Situation: A homeowner charges their elderly parent just £150/month (£1,800/year) to live in a property they own, well below the £750/month market rate for the area, while incurring £2,600/year in insurance, maintenance, and a share of mortgage interest.

Without the restriction, the homeowner might expect to show a £800 loss (£1,800 − £2,600) usable against other income.

With the uncommercial letting restriction, allowable expenses are capped at £1,800 (the rent received) — meaning the taxable profit is £0, but the £800 of "excess" expenses can't be used to reduce other income; at best, some of that excess might be carried forward against future income from the same letting, if the arrangement later becomes commercial or rent increases.

Capital Gains Tax implications

If the property was ever your own main home, letting it to family (whether commercially or below market) generally ends the period of Private Residence Relief eligibility for CGT purposes from that point, other than certain final-period exemptions. Any gain relating to the letting period, family arrangement or not, is generally taxable on eventual sale, so it's worth factoring this into any decision to let a former or potential main residence to relatives.

Practical points

• Get a formal written tenancy agreement, even for a family arrangement, to evidence the terms clearly for tax and mortgage purposes
• Confirm mortgage consent to let, since lenders require this regardless of the tenant's relationship to you or the rent charged
• Keep records of comparable market rents in the area, to demonstrate clearly whether your arrangement is commercial or below-market if HMRC ever queries it
• Consider whether the £1,000 property allowance is simpler and more beneficial than itemising restricted expenses for a modest below-market arrangement

The bottom line

Renting to family below market rent is a common and entirely legitimate arrangement, but it comes with a specific tax restriction that prevents the below-market element from generating a deductible loss against other income. Understanding this restriction, keeping good records, and confirming mortgage consent upfront avoids both an unwelcome tax surprise and a breach of your mortgage terms.