Business Use of Home: Claiming Actual Costs

Why Actual Costs Often Beat the Flat Rate

HMRC's simplified expenses method gives you a maximum of £312 per year for working from home. For many sole traders, the actual costs method produces a claim several times larger — potentially saving you hundreds of pounds more in tax.

The actual costs method requires more record-keeping, but the additional tax savings usually make it worthwhile. This guide walks you through the exact calculations.

Step 1: Identify Your Allowable Household Costs

The household costs you can include in your calculation are:

• Gas and electricity
• Water rates
• Council tax
• Mortgage interest (not capital repayments — just the interest portion)
• Rent (if you rent your home)
• Home insurance
• Broadband and internet (if not claimed separately)
• General repairs and maintenance (to the property as a whole)

You cannot include:

• Mortgage capital repayments
• Food and grocery costs
• Personal phone costs (claim these separately)
• Furnishing costs (claim equipment separately through capital allowances)

Step 2: Calculate the Business Proportion

There are two common approaches:

Method A: Room-Based Calculation

Divide the number of rooms used for business by the total number of rooms in your home, then adjust for the time the room is used for business.

Formula: (Business rooms / Total rooms) x (Business hours / Total hours available)

Example: You use one room out of five exclusively for work, 8 hours per day, 5 days per week.

• Room proportion: 1/5 = 20%
• Time proportion: 40 hours per week out of 168 hours = 23.8%
• Combined proportion: 20% x 23.8% = 4.8%

Alternatively, many sole traders and accountants use a simpler calculation:

• Room proportion: 1/5 = 20%
• Days used for business: 5/7 = 71.4%
• Combined proportion: 20% x 71.4% = 14.3%

HMRC doesn't prescribe exactly which approach to use, but the calculation must be reasonable.

Method B: Floor Area Calculation

If rooms vary significantly in size, use floor area instead:

• Measure the floor area of your business room(s)
• Divide by the total floor area of your home
• Adjust for time as above

Example: Your home is 100 square metres. Your office is 12 square metres. You use it for business 5 days per week.

• Area proportion: 12/100 = 12%
• Time proportion: 5/7 = 71.4%
• Combined: 12% x 71.4% = 8.6%

Step 3: Apply the Proportion to Your Costs

Take your total allowable household costs and multiply by the business proportion.

Example: Total annual household costs of £12,000, business proportion of 14.3%.

Annual claim: £12,000 x 14.3% = £1,716

Compare that with the simplified expenses maximum of £312 — you'd save over £1,400 more in deductions.

Worked Example: Full Calculation

Sophie is a freelance copywriter. She works from a dedicated home office 5 days per week, 48 weeks per year. Her home has four rooms (excluding kitchen and bathroom).

Annual household costs:

| Cost | Amount | |------|--------| | Gas and electricity | £2,100 | | Water rates | £400 | | Council tax | £1,650 | | Mortgage interest | £3,600 | | Home insurance | £320 | | Broadband | £480 | | Total | £8,550 |

Business proportion:

• Rooms: 1/4 = 25%
• Time: She works from home 5 days out of 7 (she doesn't use the office at weekends)
• Combined: 25% x 5/7 = 17.9%

Annual claim: £8,550 x 17.9% = £1,530

At the basic tax rate (20%), this saves Sophie £306 in income tax plus approximately £92 in National Insurance — a total saving of about £398 per year. At the higher rate, the saving would be over £600.

Shared Spaces

If you don't have a dedicated office and instead work at the kitchen table or in a living room, you can still claim — but the time proportion becomes more important.

If you use the living room as your office for 8 hours during the day and it's a family room in the evening, the time proportion reflects only the hours of business use.

Capital Gains Tax Warning

If you have a room used exclusively for business, there's a potential capital gains tax implication when you sell your home. Your main home is normally exempt from CGT under Principal Private Residence relief, but a room used exclusively for business may not qualify for full relief.

To avoid this, many advisers recommend that you use your office room for some personal purpose as well — even if it's just keeping personal books on a shelf or occasionally watching television there. This maintains its character as a room in your home that happens to also be used for business, rather than a dedicated business premises.

The risk is small for most sole traders, and the tax saved on income tax usually far outweighs any potential CGT exposure, but it's worth being aware of.

Record-Keeping

To support your actual costs claim, keep:

• All utility bills for the year
• Council tax statements
• Mortgage interest statements (your lender provides these annually)
• Rent receipts or tenancy agreement
• Insurance premium documents
• A note of your calculation method and the resulting percentage
• A simple floor plan or description of the rooms in your home

With Accounted, Penny can help you set up your home-use calculation once, then apply it automatically each month as your bills come in.

Common Mistakes

Forgetting mortgage interest. For homeowners, mortgage interest is often the largest component of the claim. Don't overlook it.

Including mortgage capital repayments. Only the interest element is allowable. Your mortgage statement separates these.

Not adjusting the proportion when circumstances change. If you move to a bigger house or start working from home more days per week, recalculate.

Being too aggressive with the proportion. A claim that one room out of two is used 100% for business, giving a 50% claim, is likely to be challenged. Keep it reasonable.

Claim the full amount you're entitled to. Start your free trial with Accounted and let Penny calculate your home office deduction.