Self-Assessment runs on a handful of fixed dates - and HMRC's penalties for missing them are automatic, steep, and land even if you don't owe a penny. This guide sets out every deadline that matters, exactly what late filing and late payment cost you, and - if you've already slipped past a date - how to limit the damage. It's part of our series of simple explainers and sits alongside our Essential Guide to Self-Assessment for the Self-Employed, which covers who actually needs

Filing a Self-Assessment tax return is a fact of life for self-employed individuals, small business owners and freelancers. Get it right and it's straightforward. Get it wrong, or leave it too late, and it becomes stressful and expensive. This guide covers who needs to file, what you'll need, how the process works step by step, and the significant change that arrived in April 2026 with Making Tax Digital. It's part of our series of simple explainers designed to make tax make