Expenses if you're self-employed
9. How to claim
Keep records of all your business expenses as proof of your costs.
Add up all your allowable expenses for the tax year and put the total amount on your Self Assessment tax return.
You don’t need to send in proof of expenses when you submit your tax return. But you should keep proof and records so you can show them to HM Revenue and Customs (HMRC) if asked.
You must make sure your records are accurate.