Self Assessment Expenses You Might Be Missing (And Legally Allowed to Claim)

When it comes to your Self Assessment, most people claim the obvious things: software, materials, maybe fuel.

However, there are a lot of legitimate business expenses that often get missed.

And missing them usually means you’re paying more tax than you need to.

The HMRC Rules:
What Counts as an Allowable Expense?

Before looking at specific expenses, it’s important to understand the rules HMRC apply.

Wholly and Exclusively for Business

An expense must be incurred wholly and exclusively for the purpose of your business.

In simple terms, if you would not have spent the money without your business, it is likely to be allowable.

Duality of Purpose

This is where many people get caught out.

If an expense has both a business and personal purpose, it may not be allowable, even if it supports your business.

A common example is everyday clothing. Even if you only wear it for work, it is still suitable for personal use, so it is not allowable.

However, where the business element can be clearly separated, that portion may still be claimed. This applies to things like phone bills and internet usage.

Apportionment

Where there is mixed use, you can claim the business proportion of the cost, as long as it is reasonable and consistent.

Typical examples include mobile phones, home working costs, and vehicle use.

Commonly Missed Expenses

Use of Home

If you work from home, even part-time, you may be able to claim a proportion of your household costs.

This can include electricity, gas, internet, and in some cases water and rent or mortgage interest.

You can either use HMRC’s simplified flat rate or calculate the actual business use.

This is one of the most commonly missed areas.

Mobile Phone and Internet

Where these are used for business, you can claim the business proportion of the cost.

This is a straightforward example of apportionment. You cannot claim the full amount if there is personal use, but you can claim a reasonable business percentage.

Mileage and Travel

If you use your personal car for business, you can claim mileage at HMRC’s approved rates.

You can claim:

• 45p per mile (first 10,000 miles)

• 25p thereafter

These are petrol/diesel rates - electric cars are different.

Alternatively, you can claim actual running costs, but you must be consistent once a method is chosen.

Other commonly missed travel costs include parking, tolls, and train fares.

Travel between home and a regular place of work is not allowable, this is considered commuting.

Professional Subscriptions and Insurance

Fully allowable if business-related:

• Trade memberships

• Professional bodies

• Insurance (PI, public liability)

Training and Courses

You can claim training that:

• Maintains or improves your current skills
  

You cannot claim:

• Training that gives you a new trade or skill
  

👉 This is another duality of purpose trap: HMRC view new skills as a personal investment, not a business expense.

Clothing

Everyday clothing is not allowable, even if worn only for work.

However, uniforms, protective clothing, and branded workwear can be claimed.

Small Equipment and Office Costs

Items such as stationery, printer ink, desk equipment, and software subscriptions are often overlooked.

Individually they may seem minor, but they can add up over the year.

Bank Charges and Payment Fees

Business bank charges and payment processing fees, such as those from Stripe, PayPal, or Shopify, are allowable.

Marketing and Advertising

This includes website costs, hosting, domain names, social media advertising, and branding or design work.

Bad Debts

If you have invoiced a customer and it is clear the amount will not be recovered, it may be written off and claimed as an expense.

Capital Allowances

Larger purchases such as laptops, equipment, and furniture may be claimed using the Annual Investment Allowance.

Final Thoughts

Most people do not miss expenses because they are doing anything wrong. They simply do not fully understand what they are allowed to claim.

As a guide:

• The expense must be wholly and exclusively for business

• Be cautious of duality of purpose

• Split costs fairly where required

• Keep clear records to support your claims
  

Getting this right means staying compliant while not paying more tax than necessary.

Need Help With Your Self Assessment?

At Hazel House, we take the time to understand your business properly, so we can spot the things you should be claiming but probably are not.

📩 If you would like your expenses reviewed properly, get in touch at clients@hazelhouse.uk or book a call.