Transcription: How the tax office works out your tax bill. This causes no end of confusion. Here's how it works. First, you take all the sources of income you got coming in. But you can ignore anything that's tax-free income such as TESAs and PEPS or not considered income such as a legacy and worry about any capital gains tax later. Let's say this figure is £39,262. Now, deduct any payments you make that get full tax relief, such as tax allowable expenses in your job. Let's say these come to £800. And then deduct full relief allowances. These are set amounts of income everyone is allowed to receive before pa ...