How expenses reduce your tax bill
Allowable expenses are deducted from your income before tax is calculated. If you're a basic-rate taxpayer, every £100 of legitimate expenses saves you £29 (20% income tax + 9% Class 4 NI). For a higher-rate taxpayer, it's £42 per £100.
That means a self-employed person on £40,000 who claims £5,000 in expenses saves £1,450 in tax. That's real money — and many people are leaving it on the table.
The expenses most people miss
1. Working from home (£312 – £1,500+ per year)
If you work from home regularly, you have two options:
- Simplified method: Claim a flat rate based on hours worked at home — 25–50 hours/month = £10/month; 51–100 hours = £18/month; 101+ hours = £26/month. No receipts needed.
- Actual costs method: Calculate the proportion of household bills (rent/mortgage interest, electricity, gas, council tax, broadband) used for business. Often works out significantly more.
2. Business mileage (up to £4,500+/year)
If you drive for business, you can claim 45p per mile for the first 10,000 miles, then 25p per mile after that. This covers fuel, insurance, wear and tear — everything. You just need a simple log of dates, destinations, and miles.
Example: A self-employed electrician driving 12,000 business miles per year can claim:
- First 10,000 miles × 45p = £4,500
- Next 2,000 miles × 25p = £500
- Total claim: £5,000 — saving £1,450 in tax (basic rate)
3. Phone and broadband
Claim the business proportion of your personal phone and broadband bills. If you estimate 40% business use on a £50/month phone contract, that's £240/year you can claim.
4. Professional subscriptions and software
Software subscriptions (accounting software, design tools, cloud storage), professional body memberships, trade magazines — all fully deductible.
5. Training and development
Courses and training that update or maintain existing skills for your current trade are allowable. A web developer attending a JavaScript conference, or a plumber doing a gas safety refresher — both claimable.
Quick savings calculator
Here's how much typical expense claims save at basic rate (29%) and higher rate (42%):
| Annual expense | Basic rate saving | Higher rate saving |
| Home office (flat rate) | £90 | £131 |
| 10,000 business miles | £1,305 | £1,890 |
| Phone & broadband (40%) | £70 | £101 |
| Software & subscriptions | £87 | £126 |
| Total savings | £1,552 | £2,248 |
What you can't claim
HMRC is strict about the line between business and personal:
- Commuting: Travel between home and your regular workplace isn't claimable (but travel to client sites and temporary workplaces is)
- Clothing: Everyday clothes aren't allowable, even if you only wear them for work. Uniforms, protective gear, and costumes are fine
- Client entertainment: Taking clients out for dinner is not an allowable expense (business meals while travelling solo are)
- Fines and penalties: Parking tickets, late filing penalties — not claimable
Explore all HMRC categories: Our Allowable Expenses Guide breaks down every claimable category with examples and tips. You can also use the Income Tax Calculator to see how expenses reduce your overall tax bill.