Allowances reduce taxable income and income tax. They work by lowering the income tax you must pay on your income subject to tax. A tax allowance refers to the amount of income not subject to tax. You are only required to pay income tax on the amount of your taxable income that exceeds the tax allowance. Allowances and reliefs that apply automatically to your tax return are subtracted from your income before tax is computed. This means you will pay less tax if you claim them. You must claim the correct allowances and reliefs to minimise your tax payment. For example, if you want to claim a marriage allowance, you must do it yourself by filling out a form and submitting it to HM Revenue & Customs every year.