If you’re a homeowner in the UK, you’ve probably heard whispers about mortgage interest tax deductions and wondered if you’re missing out on a valuable break. The reality is that for most people, the answer is a firm no — mortgage interest relief on your main home was scrapped back in April 2000. That means the average homeowner paying around £3,500 a year in interest on a typical loan gets zero tax benefit from it. I’ve been writing about property finance for years, and this is the single most common misunderstanding I come across — people assume there’s a deduction waiting for them, and they’re often disappointed when they find out there isn’t.
But here’s where it gets interesting. If you’re self-employed, run a business from home, or have a side hustle, you might be able to claim a portion of your mortgage interest as a legitimate business expense. According to HMRC, over 4 million self-assessment filers claimed home office expenses in the 2023/24 tax year — that’s up 15% from before the pandemic. The key is knowing exactly how the rules work and where the traps lie. Here’s what you actually need to know.
If you’re a landlord with a buy-to-let mortgage, the rules are different — but that’s a separate topic. For now, let’s focus on what actually works for your main home. If you’re a first-time buyer trying to make sense of all this, you might find our guide on home loan interest deductions for first-time buyers helpful as a starting point.
How mortgage interest tax relief actually works for your main home
The most important thing to understand is that there’s no universal tax break for your personal mortgage. The old system — Mortgage Interest Relief at Source, or MIRAS — let homeowners deduct interest at source, effectively reducing their monthly payments by the basic tax rate. But the government phased it out by April 2000, calling it outdated and inflationary. Since then, your mortgage interest has been treated exactly like your grocery bill or your Netflix subscription: a personal expense with no tax benefit.
Where it gets useful is if you’re self-employed, a freelancer, or run a business from home. HMRC allows you to claim a proportion of your mortgage interest as a business expense if your home is your main place of business or you have a dedicated space used exclusively for work — like a home office where you meet clients or handle admin. The key word is “exclusively.” If your spare room doubles as a guest bedroom at weekends, you can’t claim for it. If you’re thinking about buying a property with a dedicated workspace, our tips on buying a house with great construction quality might help you plan ahead.
Why this matters more than you think
The difference between claiming and not claiming can be significant. Let’s say you’re a self-employed graphic designer with a mortgage interest bill of £4,200 a year. If your home office takes up 15% of your floor space and you work from home four days a week, you could claim roughly £360 in deductible interest. At the basic rate of 20%, that saves you £72. At the higher rate of 40%, it’s £144. That’s not life-changing, but it’s real money — and it’s money you’re entitled to.
But here’s where the numbers get more interesting. If you’re a Scottish intermediate-rate payer — that’s the 21% band for income between £27,492 and £43,662 — the same £360 deduction saves you £75.60. The Scottish tax bands for 2025/26 are different from the rest of the UK, and that affects your savings. A higher earner in Scotland’s top rate of 48% would save £172.80 on the same claim. The point is: your marginal tax rate directly determines how much you actually keep.
What I tend to notice is that people either assume they can’t claim anything at all, or they think they can claim their entire mortgage interest. Both are wrong. The truth sits somewhere in the middle, and it requires a bit of maths. If you’re unsure about your specific situation, speaking to a financial advisor can help you work through the numbers without guessing.
Where people go wrong with mortgage interest claims
Claiming the full mortgage interest instead of just the interest portion
This is the most common error I see. Your monthly mortgage payment is made up of two parts: interest and capital repayment. Only the interest portion is potentially deductible — never the capital. If your annual mortgage statement shows £10,000 in total payments but only £4,000 is interest, you can only claim against that £4,000. Claiming the full amount is a red flag for HMRC and could trigger an enquiry.
Forgetting to prorate for part-time home use
If you work from home three days a week and use your office for personal stuff the rest of the time, you can’t claim the full space proportion. You need to multiply your claim by the fraction of days you actually work. For example, if your office takes up 20% of your home and you work four days a week, your deductible interest is: total interest × 20% × (4/7). A lot of people skip this step and end up overclaiming. HMRC’s guidance is clear — time use matters.
Using the simplified expenses flat rate when it doesn’t cover mortgage interest
HMRC offers a simplified expenses scheme where you can claim a flat £6 per week for home office use. That’s fine for covering heating, lighting, and internet — but it doesn’t cover mortgage interest. If you want to claim mortgage interest, you have to use the actual costs method. I’ve seen people tick the simplified box and then try to add mortgage interest on top, which doesn’t work. Stick to actuals if your mortgage interest claim is significant.
Assuming PAYE employees can claim through their tax code
If you’re employed but have a side hustle — say you sell on Etsy or do freelance writing — you can’t claim mortgage interest through your PAYE tax code. It has to go through a self-assessment tax return. I’ve had clients who missed out on hundreds of pounds in deductions simply because they didn’t realise they needed to file a return. If you have any self-employed income, even a small amount, filing a self-assessment is the only way to claim.
→ Scroll right to see all columns
| Claim Type | Who Can Use It | Covers Mortgage Interest? |
|---|---|---|
| Simplified expenses (£6/week flat rate) | Self-employed individuals | No — covers utilities only |
| Actual costs method (proportion of interest) | Self-employed with dedicated home office | Yes — based on space and time |
| Corporation tax deduction | Limited company owners | Yes — fully deductible at 25% (2025/26) |
| PAYE tax code adjustment | Employees only | No — must use self-assessment |
If you’re buying a home and want to avoid costly mistakes down the line, our article on costly mistakes UK home buyers make covers the traps that trip people up during the purchase process itself.
How to calculate and claim your mortgage interest deduction
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Measure your workspace accurately
Start by measuring the floor area you use exclusively for business. If your home office is 20 square metres and your total home is 100 square metres, your space proportion is 20%. Be honest here — if you occasionally eat lunch at your desk, that’s fine, but if the room doubles as a guest bedroom, it’s not “exclusive” use. HMRC can and does challenge claims where the space clearly isn’t dedicated to business.
Factor in your time proportion
If you work from home full-time, your time proportion is 7/7. If you work four days a week, it’s 4/7. This is where a lot of people slip up. You can’t claim for days when your office is sitting empty. Multiply your space proportion by your time proportion to get your overall claim percentage. For example: 20% space × (4/7) time = 11.4% of your total mortgage interest is deductible.
Gather your mortgage interest figures
Your lender sends an annual statement showing how much interest you paid during the tax year. You need this exact figure — not your total payments, just the interest. If you can’t find the statement, log into your online banking or call your lender. Keep a copy for your records in case HMRC asks to see it later.
Calculate and enter on your tax return
Multiply your annual mortgage interest by your combined space-and-time percentage. For example: £5,000 interest × 11.4% = £570 deductible. Enter this under “business expenses” in the self-assessment return. If you’re using accounting software, categorise it as “use of home as office” or “property expenses.” Don’t put it under “mortgage interest” — that field is for buy-to-let landlords, not home workers.
- 1Measure your workspaceCalculate the floor area used exclusively for business as a percentage of your total home. A 20 sqm office in a 100 sqm house = 20%.
- 2Factor in time proportionIf you work four days a week, multiply your space percentage by 4/7. Full-time work means 7/7.
- 3Get your annual interest figureFind the total interest paid from your lender statement. Only interest qualifies — not capital repayments.
- 4Calculate and fileMultiply interest by space% × time%. Enter the result under business expenses on your self-assessment return.
What about limited company owners?
If you run your business through a limited company, the rules are different. You can claim mortgage interest as a fully deductible business expense through corporation tax, which is 25% for the 2025/26 tax year. But there’s a catch: if the property is owned personally and you’re charging rent to your company, HMRC may treat it as a director’s loan perk. Make sure the arrangement is structured properly — a property lawyer can help you set this up without triggering unwanted tax bills.
Future changes to watch for
The tax bands and personal allowance are frozen until at least 2028, which means more people are being dragged into higher tax brackets each year. If your income creeps above £50,270, your mortgage interest deduction suddenly becomes worth 40% instead of 20%. That’s a significant difference. Keep an eye on your total income — if you’re close to a threshold, it might be worth timing your claim to maximise the benefit. The Scottish bands are also worth monitoring, as they’ve diverged further from the rest of the UK in recent years.
Frequently asked questions
Can I claim mortgage interest if I’m a PAYE employee working from home? ▾
What if my home office is also used as a guest bedroom? ▾
Does the £6 per week simplified expenses rate cover mortgage interest? ▾
I’m over 65 — is there any special allowance for mortgage interest? ▾
Can I backdate a mortgage interest claim if I missed it last year? ▾
What if I’m on an emergency tax code — does that affect my claim? ▾
Sources and Further Reading
Tips for buying land with planning permissions in the UK — If you’re considering buying land to build a home with a dedicated workspace, this guide covers the planning process and what to look for.
Property ladder myths busted: how to actually get on it in the UK — A practical look at the common misconceptions that stop first-time buyers from getting on the property ladder.
Interest and alternative finance payments eligible for relief on qualifying loans (HS340). HM Revenue & Customs, 2025.
Understanding the basics of mortgage interest tax deduction. My Tax Accountant, 2025.
Mortgage interest tax deduction UK main residence: what you need to know. Pie Tax, 2025.
