In short
Your Self Assessment return must be filed online, and any tax paid, by 31 January following the end of the tax year. For 2026/27 the personal allowance is £12,570 and the higher-rate threshold £50,270 — both frozen, which quietly pulls more of your income into higher bands each year. LMJ Group prepares and files your return, and plans ahead so you claim every relief you are entitled to.