Indietax

Use of Home as Office Calculator 2026/27

Updated for the 2026/27tax year · Last updated

country: "UK" applicableCountries: ["UK"]

If your home costs are significant — high rent, mortgage interest, or utility bills — the HMRC apportionment method for home office use can give a larger deduction than the simplified flat rate. This calculator works out the deductible amount based on the proportion of your home and time that you genuinely use for business.

Enter your home details and annual running costs below. The result is the amount you can deduct from your self-employed profits. To compare this against the flat-rate simplified method, use the Simplified Expenses Home Calculator.

Complete all fields above to see your deduction.

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How this calculator works

The apportionment method calculates your home office deduction in two steps: first, how much of your home is used for business (by rooms); second, how much of that room's time is devoted to business (by hours). Multiply the two fractions together and apply to your total annual home costs.

Step 1 — Room fraction

Count the total habitable rooms in your home, excluding bathrooms, toilets, kitchens, and hallways. Divide the number of rooms used for business into that total. A five-room house (two bedrooms, living room, dining room, study) where you use the study gives a 1/5 room fraction.

Step 2 — Hours fraction

Estimate the hours per week you use the business room for work. Divide by 168 (the total hours in a week). Working 35 hours per week in a home office gives 35 ÷ 168 = 20.8%.

Combined fraction and deductible cost

Multiply the room fraction by the hours fraction to get the overall business-use proportion. Apply that to your total annual home running costs (rent/mortgage interest, utilities, council tax, insurance). The result is the deductible amount.

What to include in total home costs

Include rent or mortgage interest (not capital repayments), gas and electricity, water, council tax, buildings and contents insurance, and broadband where it has personal and business use. Add together the annual figures for each. Do not include costs that are already wholly business (like a dedicated business phone line) — deduct those in full separately.

Mixed-use vs exclusive use

This calculator assumes the room has mixed personal and business use — you also use it in evenings, at weekends, or occasionally for personal purposes. This is the standard approach and avoids any capital gains tax complications on the eventual sale of your home. If you have a genuinely exclusive-use business room, the deduction would be calculated differently (based on rooms only, without the hours fraction) but consult an accountant before making that election, as it may affect your CGT Principal Private Residence relief.

Travel expenses too? If you drive for business, you can also claim the HMRC mileage allowance — 45p per mile for the first 10,000 business miles in a car. Both the home office deduction and mileage are claimed on the self-employment pages of your Self Assessment return.

Frequently asked questions

The apportionment method tends to give a larger deduction when your total home running costs are high — typically when you pay significant rent or mortgage interest, have high utility bills, or use a dedicated room for business for most of the week. If your annual home costs are, say, £12,000 and you use one room out of five for business for 40 hours out of 168 per week, the deductible amount is around £571 — compared to a maximum of £312 per year using the simplified rate.
You can include: rent (or mortgage interest — not capital repayments), gas and electricity, water rates, council tax, buildings and contents insurance, general repairs and maintenance (not improvements to your office specifically), and broadband or phone where it has a dual personal/business use. You apportion these costs by the fraction of your home used for business. Costs that are 100% business (a dedicated phone line, printer ink used only for work) are deductible in full outside this calculation.
No. Mortgage capital repayments are not an allowable expense — they represent building up an asset (equity in your home), not a cost of running your business. Only the interest portion of your mortgage payment is eligible. If you're unsure of the split, check your annual mortgage statement or contact your lender.
Council tax is an allowable cost to include in the total annual home costs for apportionment purposes — you're paying it partly to support the infrastructure your business uses. Include your annual council tax in the total home costs field alongside utilities and rent/mortgage interest. The apportioned fraction of it will be deductible.
If you claim a room as used exclusively for business — meaning you never use it for any personal purpose — the deduction can be larger, but it creates a capital gains tax risk. The Principal Private Residence (PPR) relief that exempts your home from CGT on sale may be partially denied for the room used exclusively for business. The apportionment method in this calculator assumes mixed personal/business use, which avoids this CGT complication. Most accountants recommend mixed-use to protect PPR relief unless the business use is genuinely exclusive and the CGT risk is understood.
You divide the number of rooms used for business by the total number of rooms in your home, excluding bathrooms, kitchens, hallways, and other non-habitable spaces. A four-bedroom house with a living room and dining room has six rooms; using one as an office gives a one-sixth room fraction. If you use two rooms, it's two-sixths (one-third). The calculator handles this arithmetic automatically.
A week has 168 hours. The hours fraction is the number of hours per week you use the room for business, divided by 168. Working 40 hours a week in a home office gives 40/168 ≈ 23.8%. This fraction is then applied to the per-room annual cost to give the deductible amount. Using more hours — even on evenings or weekends — increases the fraction legitimately.
No. For the same property, you use one method or the other for a given tax year. You can switch between methods from year to year. Most self-employed people compare both figures (this calculator and the Simplified Expenses Home calculator) and choose whichever gives the larger deduction for that particular year.

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