Self Assessment
PayToolkit's self assessment articles: practical UK tax guidance, worked examples, and links to the right free calculator for each topic.
Self Assessment catches a lot of people off guard — not just the self-employed, but landlords, side-hustlers, and anyone with untaxed income over the reporting thresholds. Missing the 31 January deadline brings an automatic £100 penalty even if you owe nothing, and interest builds daily after that on any tax due. Our Tax Set-Aside Calculator tells you how much to put by from every payment you receive, so the January bill is never a surprise.
If you're not sure whether you even need to file, start with when you need to register for Self Assessment. Already registered and want to check what you owe right now? Use the Take-Home Pay Calculator for employment income or the Sole Trader Tax Calculator for self-employed profits, and track everything year-round with the free Expense Tracker.
How to Calculate Your Self Assessment Tax Bill 2026/27
Step-by-step guide to working out your Income Tax, Class 2 and Class 4 NICs, payments on account and key deadlines for 2026/27.
Self AssessmentSelf Assessment Checklist 2026/27: Documents, Deadlines & Steps
Everything you need to gather before filing your tax return. All documents, deadlines, and step-by-step filing guidance for 2026/27.
Tax TipsPayments on Account Explained: Why HMRC Wants Tax in Advance
Understand how advance tax payments work, who needs to make them, and how to reduce them if your income has dropped.
Self Employed5 Tax Mistakes Self-Employed People Make (And How to Avoid Them)
From missed deadlines to wrong expenses, learn the five most common tax mistakes that cost self-employed people hundreds in penalties and lost tax relief.