How Much Tax Are You Overpaying Because of These 7 Missed Expenses?

Most sole traders claim the obvious expenses software, equipment, maybe some travel. What they rarely claim are the quieter ones. The flat-rate home office allowance that needs no receipts. The professional registration fee paid annually from a personal account and forgotten by January. The phone bill where the business proportion sits unclaimed because the phone is also personal. The pre-trading laptop bought a month before the first invoice that HMRC would happily allow but nobody thought to include. These are not fringe cases. They are the expenses that sit legitimately on most sole traders' returns, unclaimed, every single year. At a combined income tax and Class 4 NI rate of roughly 26 percent for a basic rate taxpayer, every £100 of missed expenses costs approximately £26 in unnecessary tax.

Dan left his corporate IT job in Sheffield in April 2025 and went self-employed as a consultant. Sixteen months in, with January 2027 approaching, he sat down to total up his expenses. He came up with around £3,000. He was not being careless. He was just claiming what felt obvious, the CPD course he attended in June, the software subscription he paid monthly. What he was not claiming was everything else. By the time he had worked through all seven categories below, his actual allowable expenses came to £7,862. The difference £4,862 of unclaimed costs was costing him £1,264 in unnecessary tax.

The expenses below are the ones Dan missed. They are also the ones most commonly left off sole trader returns across almost every profession and business type.

1. Mileage — 45p Per Mile for 2025/26

Mileage is the most consistently under claimed expense on sole trader returns. The reasons vary; no log was kept, the rate was not known, the journeys felt too informal to count. None of these is a reason to leave the claim off the return.

The confirmed HMRC approved mileage rate for 2025/26 is 45p per mile for the first 10,000 business miles and 25p above that. This single rate covers all vehicle running costs; fuel, insurance, servicing, depreciation. You cannot claim mileage and also claim fuel separately. But if you claim mileage, you never need a receipt for any of those costs. The mileage figure and the rate are the only things you need.

Business miles are any miles driven for business purpose to clients, to suppliers, to networking events, to training, to the post office to send stock. The commute from home to a fixed regular place of work does not count. Everything else broadly does.

Amara Foster left her NHS role in September 2025 and went fully self-employed as a physiotherapist. She drove to home visits across Bristol throughout the year; four or five patients a day, three days a week, covering the city and surrounding areas. She never kept a mileage log because she was focused on the clinical work and assumed the paperwork could wait. By the time January arrived she had a rough sense that she had driven a lot but no figure attached to it.

Working back through her patient appointment calendar and the distances to regular patient postcodes, she reconstructed approximately 6,200 business miles for the year. At 45p per mile that is £2,790. At a 26 percent combined tax and NI rate, the tax saving is £725. From a calendar and ten minutes on Google Maps.

Note on the rate. HMRC increased the mileage rate to 55p from 6 April 2026. The higher rate applies from the 2026/27 tax year onwards. For the 2025/26 return the correct rate is 45p. Using the wrong rate is one of the most common errors on sole trader mileage claims particularly for anyone who started researching their return after the rate change was announced.

What to do if you kept no mileage log. Reconstruct from calendar appointments, client visit records, diary entries and a realistic estimate of regular journeys. An honest reconstruction with a brief written note of the basis is more credible than a zero. For more on reconstructing records without a log, the guide to filing Self Assessment with no records covers the approach in full.

Dan's missed mileage: 4,200 miles × 45p = £1,890. Tax saving missed: £491.

2. Home Office: £6 Per Week, No Receipts Required

HMRC's simplified home office allowance is £6 per week for anyone who works from home regularly. That is £312 for the full year. No receipts. No calculation of actual costs. No need for a dedicated office room.

The allowance applies if you work from home for at least 25 hours per month. For most sole traders who work from home — whether full time or part time — this threshold is easily met. You do not need to own the property. You do not need a separate room. You just need to work from home with some regularity.

Most sole traders who work from home either do not know the allowance exists or assume it requires a formal home office setup. Neither is true. A kitchen table where client calls are taken and work is done qualifies. A spare bedroom used as a workspace qualifies. The allowance is there specifically because HMRC recognises that home-based working has real costs: heating, lighting, broadband and designed a simple flat-rate claim to avoid the complexity of calculating actual proportions.

Dan worked from home full time. Every client call, every deliverable, every proposal was produced from his home office in Sheffield. He claimed nothing for it because he assumed the calculation would be complicated. The actual claim: £6 per week × 52 weeks = £312. He needed to know the rate existed and enter a single figure.

The alternative method. If your actual home costs rent or mortgage interest, council tax, heating, lighting, broadband are high and you use a significant proportion of your home exclusively for business, the actual proportion method may produce a larger claim than £312. The calculation is more complex but the result can be substantially higher for someone running a business from a dedicated studio or workshop at home. For most desk-based sole traders, the flat rate is simpler and sufficient.

You can read more about how to claim home office expenses here

Dan's missed home office claim: £312. Tax saving missed: £81.

3. Phone and Broadband: The Business Proportion

If your phone is used for both personal and business calls, the business proportion of the cost is an allowable expense. The personal proportion is not. This is the wholly and exclusively rule applied practically — you cannot claim a dual-use expense in full, but you can claim the business share.

The key is arriving at a reasonable business proportion and applying it consistently. There is no prescribed method. HMRC expects an honest estimate based on actual usage not a figure chosen for convenience.

A sole trader who uses their phone 60 percent for business purposes and pays £600 per year on their contract can claim £360. If the same phone is on a £50-per-month plan, that is £720 annual cost and a £432 deductible expense at 60 percent. The same logic applies to broadband — the proportion used for business is deductible, provided business use is genuine and the proportion is honest.

Dan used his phone constantly for client calls, video meetings and project management. He estimated 65 percent business use conservative, given his work pattern, but defensible. His annual contract was £588. His deductible proportion: £382.

Most sole traders claim nothing on their phone because the dual-use element feels like it disqualifies the claim. It does not. It qualifies the proportion. You can read more on mobile expenses here

Dan's missed phone claim: £360 (rounded from £382 for simplicity). Tax saving missed: £94.

4. Professional Subscriptions and Memberships

Industry body memberships, professional registration fees, trade association subscriptions — these are allowable expenses where the membership is relevant to the trade being carried out.

This category is missed for one consistent reason: the fees are paid annually, often by direct debit from a personal account in a quiet month, and they are forgotten entirely by the time January arrives.

Amara's HCPC registration, the statutory registration required to practise as a physiotherapist is an allowable expense. Her Chartered Society of Physiotherapy membership is an allowable expense. Her professional indemnity insurance premium is an allowable expense. Combined, these came to £890 for 2025/26. She had claimed none of them on her previous return, the one she filed when she was still employed because she had not been filing self-employment expenses. In her first year of full self-employment, she almost missed them again simply because they were paid from her personal account and did not appear on her business bank statements.

Dan's professional body membership relevant to his IT consulting practice was £480 for the year. One annual payment. One forgotten allowable expense.

The test for professional subscriptions. HMRC's approved list covers most major professional bodies. If the membership is on the approved list, the fee is automatically allowable. If it is not on the list, the question is whether the membership is relevant to the specific trade being carried out. A membership that is relevant to Dan's IT consulting practice but not to a general non-technical business would be allowable for Dan but not for a sole trader in an unrelated field.

Dan's missed subscriptions: £480. Tax saving missed: £125. Amara's missed subscriptions and registration fees: £890. Tax saving missed: £231.

5. Training and Professional Development

Courses, books, trade publications and online learning directly related to the existing trade are allowable expenses. This is one of the most misunderstood categories in sole trader tax — because the rule has a sharp edge that people either miss entirely or apply too broadly.

The test is whether the training relates to the trade already being carried out — not to a new trade or a new qualification being sought. An IT consultant buying a course that develops skills in their existing discipline can claim it. The same person studying for a qualification to move into an entirely different field cannot — that is a capital expense on a new trade, not a revenue cost of the current one.

Within that boundary, the allowable territory is broader than most people assume. CPD courses required by a professional body. Books directly related to the trade. Specialist trade publications. Online platforms used for continuing professional development. Software tutorials for tools used in the business.

Amara claimed her CPD courses she attended two physio-specific continuing development workshops totalling £680 during 2025/26. She claimed them correctly.

What she did not claim was her professional journal subscription , £148 per year because she had always thought of it as personal reading. For a practising physiotherapist, a clinical journal directly relevant to her practice is an allowable expense. The subscription went in as an amendment to her draft return before filing.

The pre-trading angle. There is a specific application of this rule that almost nobody knows. If you attended training before you started trading — in preparation for the business you were about to start — and the training would have been allowable if the business had already been trading, it can be claimed on your first Self Assessment return. This applies to any training incurred within seven years before the start of trading.

Dan's claimed training: £340 (CPD course in June 2025). Already on the return. Amara's missed journal subscription: £148. Tax saving missed: £38.

6. Bank Charges and Payment Processing Fees

Every fee charged on a business transaction is a deductible expense. Bank account fees for a business account. PayPal transaction charges. Stripe processing fees. eBay and Etsy selling fees. Vinted, Depop and Amazon platform fees.

This category is missed with remarkable consistency — and for a logical reason. The fees are deducted automatically before the payment arrives. The sole trader sees the net receipt, not the gross sale and the fee. The fee never feels like a separate expense because it never sat in the account as money before being paid out.

For a sole trader processing £30,000 of payments through Stripe at 2.9 percent plus 30p per transaction, the total processing fees over the year could easily reach £900 or more. For an eBay seller with £31,000 of gross sales, platform fees at roughly 12 to 15 percent of gross sales represent £3,700 to £4,650 of allowable deductions.

These are not small numbers. And they are consistently left off returns because the seller declares the net payout , what arrived in their bank account after fees as their income, which both understates gross income and ignores the fees as a separate expense. The correct approach is to declare gross income and claim fees separately.

Dan's consulting work involved Stripe payments from clients who preferred card billing. His total Stripe processing fees for 2025/26 came to £620. They were deducted automatically on every transaction and never appeared as a separate outgoing. He had not thought of them as an expense at all.

The link to platform sellers. If you sell on platforms and are unsure whether to declare gross income or net payouts, the guide to filing Self Assessment with no records covers the gross versus net distinction and the DAC7 reporting position in detail.

Dan's missed payment processing fees: £620. Tax saving missed: £161.

7. Pre-Trading Expenses: The Rule Almost Nobody Knows

This is the most valuable entry on this list for first-year sole traders and the one that receives almost no coverage anywhere.

HMRC allows expenses incurred before a business starts trading to be claimed on the first Self Assessment return. The conditions are that the expenses were incurred within seven years before the start of trading and that they would have been allowable if the business had already been trading at the time they were paid.

In practice, this means the laptop bought in February before the first April invoice. The website built and paid for in March before the business launched. The professional software subscription started six weeks before the first client. The equipment purchased to set up the home office before trading began. All of these are potentially claimable on the first return as though the business had been trading at the point they were bought.

Dan bought a new laptop in March 2025, one month before he left his corporate job and started consulting. He paid £1,200 for it. He assumed it could not be claimed because he had not technically started trading when he bought it. He was wrong. The laptop was bought in preparation for the consultancy he was about to start, it would have been an allowable capital expense if he had already been trading, and it was incurred within seven years of the start of trading. It was claimable in full through Annual Investment Allowance on his first Self Assessment return.

What counts as the start of trading. HMRC typically considers a business to have started trading when it first actively seeks customers, not necessarily when it receives its first payment. For most sole traders, this is the date they first started promoting services, attending client meetings or building the infrastructure of the business. Dan's first client meetings were in late March 2025, making the laptop genuinely pre-trading but within the allowable window.

Dan's missed pre-trading claim: £1,200 (laptop via Annual Investment Allowance). Tax saving missed: £312.

Two More Worth Knowing: Amara's Additional Claims

Amara's expense list looks different from Dan's. She is a physiotherapist, not a tech consultant. But the pattern is identical — expenses sitting legitimately on her return, unclaimed, because nobody had told her they were there.

Her HCPC registration fee of £90, her CSP membership of £161, her professional indemnity insurance of £680, her CPD workshops totalling £680, her clinical journal subscription of £148 and her mileage of £2,790 across 6,200 home visit miles were all allowable expenses for 2025/26. The first time she sat down and worked through each category properly, her total allowable expenses came to £4,549 — against the £680 she had originally intended to claim for the CPD workshops alone.

The tax saving on the additional £3,869 of expenses she had missed: just over £1,000.

Different profession. Same problem. The expenses were there. They just needed to be found.

For self-employed professionals with profession-specific costs — physiotherapists, teachers, IT consultants, healthcare workers — the expense categories that matter most are those specific to the registration, protection and development requirements of the profession. These are exactly the ones most commonly missed. And they are exactly the ones the 70-category Expense Tracker in the UK Sole Trader Tax Calculator 2025/26 is built to capture.

The One Rule That Covers All Seven

Every expense above passes the same HMRC test: wholly and exclusively for the purposes of the trade.

Wholly and exclusively does not mean the expense can have no personal element whatsoever. It means the reason for incurring the expense must be entirely business. A phone used for business calls and personal calls is dual-use — claim the business proportion. A laptop bought to run a consultancy and occasionally used for personal browsing is primarily business claim the full cost through Annual Investment Allowance if it qualifies. A professional membership relevant to the trade has no personal element at all claim it in full.

The test is applied at the level of purpose, not of use. Why was this cost incurred? If the honest answer is primarily or entirely for the business, the expense is claimable.

If you are unsure whether a specific expense qualifies, the question to ask is: would I have incurred this cost if I were not running this business? If the answer is no or not to this extent, the expense is likely allowable at least in part.

The seven expenses above are not the complete list of what sole traders can claim. They are the ones that sit unclaimed most often, across most professions, for reasons that have nothing to do with eligibility and everything to do with not knowing they were there. Dan's £1,264 and Amara's £1,000 were not saved by clever tax planning. They were saved by knowing what to look for.