Can I claim expenses I paid for before I registered my business?

Often yes. Pre-trading expenses incurred in the run-up to starting, within a reasonable window beforehand, can usually be claimed as if they were incurred on your first day of trading, provided they meet the same wholly and exclusively test. Keep the receipts and the dates.

What happens if I claim something HMRC later disagrees with?

If it is a genuine misjudgement on a reasonable claim, the usual outcome is simply a correction and any extra tax due, sometimes with interest. Problems escalate when claims look deliberate or the record-keeping cannot support what was claimed, which is why accurate categorisation matters more than aggressive categorisation.

Do I need a receipt for every single expense?

For anything HMRC could reasonably ask about, yes, keep some form of evidence, a receipt, an invoice, or a bank record with a clear note of what it was for. Simplified flat rates, like the home-working allowance, are the exception, since they are designed to remove that admin.

My accountant before you just filed what I gave them without asking questions. Is that normal?

It is common, but it is not what I do. Filing whatever arrives without checking it against the actual rules is how both over-claiming and under-claiming happen, quietly, for years. Part of what a discovery call does is show you the difference.

What Can I Actually Claim as a Business Expense?

If I had to name the one question every single new enquiry asks me, in some form or another, it is this one. Sometimes it arrives as "what can I put through the business?" Sometimes it is more anxious than that, someone who has been guessing for two years and is now worried HMRC is about to tell them they guessed wrong. Either way, it is the right question to ask, and it deserves a proper answer rather than a vague one.

So here is the general rule HMRC actually uses, and then the categories where I see people either miss money they were entitled to, or claim things they were never entitled to in the first place.

The rule behind every single claim

HMRC's test is that a cost must be incurred "wholly and exclusively for the purposes of the trade." Three words, and they carry the whole thing. Wholly and exclusively. Not partly. Not "well, I was thinking about work at the time." The cost has to exist because of the business, not merely alongside it.

That sounds strict, and it is, but it is also more generous than most people assume. It does not say the expense has to be essential, or that a cheaper option was available, or that you enjoyed it. It just has to be for the trade. A laptop bought purely to run your business passes. A laptop your teenager also uses for gaming does not pass cleanly, because it is no longer exclusive, though there are sensible ways to apportion mixed-use costs, which I will come back to.

Where people go wrong is usually one of two directions. Either they are too cautious, and quietly absorb costs personally that they were entitled to claim, which just means paying more tax than necessary. Or they are too loose, and claim things that would not survive a second look, which is the version that causes real problems later. Neither serves you. The aim is accuracy, not maximum aggression.

Working from home

This is the one I get asked about most, and the one people most often under-claim. If you work from home, you have two routes. The simplified flat rate is based on hours worked from home each month: £10 a month for 25 to 50 hours, £18 a month for 51 to 100 hours, and £26 a month for 101 hours or more. It is deliberately easy, no receipts, no calculations, and for a lot of sole traders it is close enough to fair that it is not worth the extra admin of doing it properly.

The alternative is working out an actual proportion of household costs, heating, electricity, broadband, based on the space used and time spent. That can be worth more if you have a dedicated office room and genuinely high running costs, but it needs to be defensible, not a number you liked the look of. I help clients work out which route actually suits their situation rather than defaulting to whichever sounds easier.

Mileage and vehicles

If you use your own car for business trips, HMRC's approved mileage rates changed from 6 April 2026, rising to 55p a mile for the first 10,000 business miles in the tax year, and 25p a mile after that. That is a meaningful increase from the old 45p rate, and I have already seen clients undervalue their claim simply because they still had the old figure in their head. If your business owns the vehicle outright, the treatment is different again, so this is one area worth checking rather than assuming.

What mileage does not cover is your ordinary commute. The trip from home to a regular place of work is not a business journey, however inconvenient that feels. Travel to a client site, a temporary workplace, or between jobs in the same day generally is.

Subsistence versus entertaining, and why the distinction matters

This is the area that catches people out the most, because the two feel similar and are treated completely differently. A meal on a genuine business trip away from your normal pattern of work, subsistence, is generally allowable. Taking a client out for lunch or drinks, client entertaining, is not deductible for tax purposes, full stop, no matter how directly it was linked to winning the work.

Staff entertaining sits differently again. There is a £150 per head exemption for annual staff events, a summer do or a Christmas party, provided it is open to all staff and the cost per head stays within that limit including VAT. Go a penny over and the whole amount becomes taxable, not just the excess, so it is worth knowing where that line sits before you book anything.

Small gifts to staff also have their own rules. Trivial benefits, gifts costing £50 or less, not cash, not a reward for performance, are generally tax free. If you are a director of a close company, there is an annual cap of £300 on how much of this you can receive.

Equipment, tools and capital allowances

Bigger purchases, computers, machinery, tools, vans, tend to fall under capital allowances rather than being deducted as a straightforward expense. For most businesses this is not something to worry about in practice, because the Annual Investment Allowance currently lets you claim the full cost against profits in the year of purchase, up to £1 million. Unless you are investing well beyond what most sole traders and small limited companies spend in a year, the effect is the same as an outright deduction, it is just filed under a different heading.

Training and professional development

Training that maintains or updates skills you already use in the business is generally allowable. Training that gives you a genuinely new skill or qualification, taking you into a different trade altogether, is treated more cautiously by HMRC and is often not deductible. A bookkeeper doing a course to stay current on software changes is on solid ground. A bookkeeper training to become a solicitor is a different question entirely.

Where I'd point you next

Every one of the categories above has edge cases, and your specific situation, sole trader, limited company, property business, whether you have staff, will change the detail even where the principle stays the same. That is exactly why I built the free expense checker tool. Tick the boxes that describe your business and it will show you the categories most likely to apply to you, as a starting point for the conversation rather than the final word.

And if you want the final word, that is what I am for. I do not charge for a first conversation, and I would rather spend twenty minutes explaining what applies to your situation now than have you find out the hard way in three years. You can book a free discovery call or just email me directly. Either way, you will leave the conversation actually understanding your own numbers, not just having them filed. That is the whole point.