7 Expenses Small Business Owners Forget They Can Claim
Written and reviewed by Zoe, Managing Director at Kernow Accountancy : our family-run Helston practice has been advising Cornish sole traders, landlords and small businesses since 2011.
Seven commonly forgotten allowable expenses that can reduce your tax bill, from home working and mileage to bad debts and pre trading costs.
If you're a sole trader or limited company owner in Cornwall, there's a good chance you're paying more tax than you need to, not because you're doing anything wrong, but because nobody ever handed you the full list of what counts as an allowable expense.
Every year we see the same thing: business owners who've been trading for years, quietly missing deductions they were entitled to the whole time. Below are the ones that come up most often.
1. Working from home
If you do any work from home, even just admin, invoicing, or the odd client call, you can claim a portion of your household costs. HMRC offers a simplified flat rate method based on hours worked from home each month, or you can calculate the actual proportion of your bills (heating, electricity, internet, mortgage interest or rent) that relates to business use. For most small business owners, the flat rate is simpler and still worth claiming; but if you use a whole room predominantly for work, calculating the real proportion is sometimes worth more.
2. Professional subscriptions and training
Membership fees for approved professional bodies, and training courses that maintain or improve skills you already use in your business, are usually allowable. This trips people up because it feels like a personal development cost rather than a business one, but if the course relates to what you already do, it counts. Training for a completely new trade or profession is treated differently, so this is worth checking case by case.
3. Business mileage
If you use your own car for business journeys, visiting clients, collecting supplies, travelling between sites, you can claim mileage at HMRC's approved rates rather than trying to apportion the actual running costs of the vehicle. It's simpler to track and often more valuable than people expect, especially for trades and mobile services where driving is a daily part of the job.
4. A proportion of your phone and broadband
If you use your personal mobile or home broadband for business as well as personal use, you can claim the business use proportion of the bill. Keep a record of how you've worked out the split; even a simple estimate based on typical usage is better than nothing, and it needs to be justifiable if HMRC ever asks.
5. Bad debts
If a client hasn't paid an invoice and you've genuinely written it off as unrecoverable, that amount can usually be claimed against your profits. A lot of business owners simply absorb the loss without realising there's a way to offset it; don't eat the loss without checking first.
6. Business entertainment (in specific circumstances)
Client entertainment itself is largely not deductible for tax purposes, but staff entertainment, like a Christmas party or team meal, usually is, up to certain limits. It's an easy one to get backwards, so it's worth checking which category any given cost falls into before assuming either way.
7. Pre trading expenses
Costs you paid out before your business officially started trading, setting up a website, buying initial stock or equipment, registering domains, can often still be claimed, as long as they were incurred wholly for the purpose of the business and within a reasonable period before you started. A lot of new business owners don't realise this window exists and simply never claim these costs at all.
Why this keeps happening
None of these are obscure or unusual; they're standard, well established allowable expenses. The reason they get missed so often isn't complexity, it's simply that nobody ever sits down and goes through the full list with a new business owner. Bookkeeping software will record what you tell it to record; it won't tell you what you've forgotten to include.
What to do next
The safest way to know exactly what you're entitled to claim, and what doesn't apply to your specific situation, is to go through your accounts with an accountant who knows your business, rather than relying on a generic list (including this one). For a more detailed look at sole trader deductions, see our guide to allowable expenses sole traders miss.
If you'd like us to take a proper look at what you might be missing, get in touch with the team at Kernow Accountancy.
This article is for general guidance and reflects UK tax rules as of 2026/27. It isn't a substitute for advice tailored to your specific circumstances; speak to your accountant before making decisions based on it.
