The expenses self-employed people forget to claim (and what they cost you)
Most people who overpay tax as a sole trader are not making a dramatic mistake. They are forgetting eight or nine ordinary costs that never got labelled as business. Here is the list, and what each one is actually worth.
Nobody sits down and decides to overpay tax. What happens is smaller and much more boring: a card gets used for a work thing on a Tuesday, it never gets labelled, and eleven months later it is one line in a list of four hundred that all look the same.
Do that thirty times a year and you have handed HMRC a few hundred pounds you did not owe.
Here is what actually gets missed, in rough order of how often.
1. Subscriptions on a personal card
The single most common one. Adobe, Notion, Canva, cloud storage, a domain renewal, a stock photo plan, the AI tool you signed up for in March. Each is small, each renews quietly, and because it went on a personal card it never entered the business records at all.
These are usually fully allowable if they are for the business. Ten subscriptions at £12 a month is £1,440 a year. At the basic rate that is £288 of tax.
2. The business share of your home
If you work from home you can claim a share of your rent or mortgage interest, council tax, electricity, gas and water. The share, not the bill. People get this wrong in both directions. Some claim nothing at all because they assume it is not allowed. Others claim the whole electricity bill, which is an over-claim and the kind of thing that invites questions.
You have two routes. Work out a reasonable proportion based on how many rooms you use for work and how much of the time, or use HMRC's simplified expenses flat rate based on hours worked from home. The flat rate is easier and safer. A proper proportion is often worth more.
3. Phone and broadband
Same principle, different ratio. Most self-employed people use their mobile far more for business than they use their gas supply, so the business share is usually much higher. It is still a share, not the full contract, unless the line genuinely is business-only.
4. Travel that was not obviously travel
Train tickets, parking, congestion charge, a taxi to a client, mileage in your own car, accommodation for a work trip. The obvious ones get claimed. What gets missed is the £4.80 here and the £12 there, spread across a year, none of which felt worth recording at the time.
Commuting to a regular place of work is not allowable. Travel to a client, a supplier, a job or a course generally is.
5. Tools and equipment
A laptop, a monitor, a chair, a drill, a camera lens. Larger purchases usually qualify for the Annual Investment Allowance, which lets you deduct the full business cost in the year you bought it. If you also use the thing personally, you claim the business share.
The ones that get missed are the mid-sized purchases. Nobody forgets a £1,400 laptop. Plenty of people forget a £64 office chair from a DIY shop.
6. Professional fees and insurance
Accountant fees, legal advice for the business, professional indemnity or public liability insurance, membership of a professional body relevant to your trade. All ordinarily allowable, all easy to forget because they are annual and land once.
7. Bank and payment charges
Business account fees, card machine fees, Stripe and PayPal percentages, currency conversion costs if you invoice abroad. Individually trivial. Across a year of taking payments online, not trivial at all.
8. Training that maintains your skills
Courses, conferences and materials that keep your existing skills current are generally allowable. Training to break into an entirely new trade usually is not. The line is not always obvious, so it is worth asking about anything expensive.
What this is worth in real money
Take the expense and multiply by your marginal rate. That is the number.
At the 20% basic rate, £1,000 of forgotten costs is £200 of tax you did not need to pay. At 40% it is £400. Self-employed National Insurance can push the real saving higher still.
The reason the total gets big is that these are not one-offs. A subscription you missed this year is one you probably missed last year too.
How to actually find yours
Reading four hundred transaction lines by hand does not work. People have tried, which is why the same costs get missed year after year.
The practical version is to let something read the statement for you and flag the lines that look like allowable costs, with a reason attached so you can judge each one. You still make the call on what was genuinely business. You just stop doing the finding by eye at 11pm in January.
You can run a bank statement through Forensix free, with no account and nothing stored, and see what comes back on your own spending. It reads each line against UK and Spanish deduction rules and tells you what is not claimed and roughly what it is worth in tax.
Whatever you use, do it before you file rather than after. Amending a return is possible but the time limits are not generous, and it is a lot more work than getting it right the first time.
General information, not tax advice. Rules and rates change, and what counts as business use depends on your own circumstances. Confirm your position on GOV.UK or with an accountant.
Frequently asked questions
What expenses can I claim as a UK sole trader?
Costs incurred wholly and exclusively for your trade: software and subscriptions, business travel and accommodation, tools and equipment, stationery and postage, professional and legal fees, business insurance, bank and payment charges, advertising, training that maintains your existing skills, and the business share of your home and phone.
Can I claim my home electricity and internet if I work from home?
You can claim the business proportion, not the whole bill. Either work out a reasonable share based on rooms used and time spent working, or use HMRC's simplified expenses flat rate based on hours worked from home each month. You cannot claim the full household bill.
How much is a missed deduction actually worth?
It is worth the expense multiplied by your marginal tax rate. At the 20% basic rate a forgotten £500 of costs is £100 of tax. At 40% it is £200. National Insurance can add more on top, so the real figure is usually higher than people assume.
Can I claim expenses from previous years I forgot?
You can normally amend a Self Assessment return for a limited period after the filing deadline, and there are separate routes for going further back. It is not unlimited, so the sooner you spot it the better. Check the current time limits on GOV.UK or ask an accountant.
Do I need a receipt for every expense?
You need to be able to show what you spent and why it was for the business. Bank and card statements are evidence of payment, but a receipt or invoice is what shows what was actually bought. Keep both where you can.