Finance⏱ 5 min read
How to Calculate the Home Office Tax Deduction (UK)
Working from home can legitimately reduce your tax bill — but the rules differ for employees, the self-employed, and those using a dedicated room. Here is the exact calculation for each situation.
The home office deduction is one of the most widely available and under-claimed tax reliefs. HMRC has simplified the rules, but the correct method depends entirely on your employment status.
Employees: Working From Home Allowance
If your employer requires you to work from home:
Fixed rate relief: £6/week (£312/year) — no receipts needed
Available regardless of actual costs.
Claim via Self Assessment or P87 form if not using Self Assessment.
Applies from the day you started working from home.
If your actual costs are higher than £6/week:
You can claim the actual additional cost (more complex — needs evidence)
Fixed costs (mortgage, council tax, insurance):
These are NOT claimable by employees — they exist regardless of WFH.
Additional costs only:
Heating, electricity, broadband (additional usage only)
£6/week HMRC flat rate is meant to cover these.
Self-Employed: Simplified Expenses Method
HMRC flat rates based on hours worked at home per month:
25-50 hours/month: £10/month
51-100 hours/month: £18/month
101+ hours/month: £26/month
Annual claims:
25-50 hrs: £120/year
51-100 hrs: £216/year
101+ hrs: £312/year
No records of actual costs needed with this method.
Available if you use your home for business (not dedicated room only).
Self-Employed: Actual Cost Method
More work, but can claim more if costs are high.
Step 1: Calculate proportion of home used for business
Method A: Number of rooms used for work / Total rooms
Method B: Floor area of workspace / Total floor area
Step 2: Calculate proportion of time used for business
Hours worked at home per week / Total hours in week (168)
Step 3: Apply dual calculation
Business use % = Room proportion x Time proportion
Example: 4-bedroom house, 1 room used as office
Work: 35 hours/week
Room proportion: 1/4 = 25%
Time proportion: 35/168 = 20.8%
Business proportion: 25% x 20.8% = 5.2%
Annual household costs:
Rent: £14,400, Utilities: £2,400, Council tax: £1,800
Total: £18,600
Claimable: £18,600 x 5.2% = £967/year
Dedicated Home Office (Self-Employed)
If a room is used EXCLUSIVELY for business:
Can claim full room costs based on floor area proportion only.
Example: 180 sqft office in 1,200 sqft house = 15% of home
Annual costs:
Mortgage interest: £8,400 x 15% = £1,260
Utilities: £2,400 x 15% = £360
Insurance: £600 x 15% = £90
Total claimable: £1,710/year
Warning: exclusive business use can create a capital gains
tax liability when you sell the property (portion of gain
attributed to the business room may not qualify for
Private Residence Relief). Consult a tax professional
before claiming this for mortgaged properties.