What expenses can I claim as a self-employed person?

You can claim allowable business expenses that are 'wholly and exclusively' for the purposes of your trade, which typically includes things like office costs, business travel, stock and materials, staff costs, insurance, marketing, professional fees and training directly related to your work. These are deducted from your income before you calculate the profit you pay tax on, so good record-keeping directly reduces your tax bill. If you're ever unsure whether something qualifies, it's safer to ask an accountant than to guess, as claiming personal or dual-purpose costs incorrectly can trigger HMRC queries.