Your first Self Assessment

Self Assessment is how HMRC collects tax on income that isn't taxed automatically through an employer's payroll. If some of your income arrives untaxed, you tell HMRC about it once a year and pay what's due.

Do you even need to file?

You typically need to complete a return if, in a tax year, you were any of the following:

• Self-employed as a sole trader and earned more than the £1,000 trading allowance.
• A partner in a business partnership.
• A landlord receiving rental income above the property allowance.
• In receipt of significant untaxed income — for example dividends, savings, or foreign income.
• A higher earner, or affected by the High Income Child Benefit Charge.

This isn't the full list, and the thresholds can change. If you're unsure, it takes us two minutes to tell you whether you need to file.

The deadlines that matter

• 5 October — register for Self Assessment if it's your first time and you need to file for the previous tax year.
• 31 October — deadline if you file a paper return.
• 31 January — deadline to file online, pay the tax you owe, and make your first payment on account.
• 31 July — second payment on account, if you make them.

Miss the filing deadline and HMRC charges an automatic penalty even if no tax is due, so the dates matter more than people expect.

What you'll need to gather

• Your Unique Taxpayer Reference (UTR) and a Government Gateway account.
• Records of all income — invoices, bank statements, dividend vouchers, P60/P45 if employed too.
• Records of allowable business expenses (see our allowable expenses guide).
• Details of pension contributions, Gift Aid donations and student loan repayments.

Common first-timer mistakes

• Leaving registration until January — the UTR can take time to arrive.
• Forgetting payments on account, then being surprised by the January bill.
• Mixing personal and business spending, which makes expenses hard to evidence.
• Guessing at figures rather than keeping clean records through the year.

The simple way to do it

Most of our clients would rather not learn the Self Assessment system at all — so we do it for them. You answer a few plain questions, we prepare and check the return, and we file it with HMRC on your behalf, well before the deadline.

Last reviewed: 2026 · Maze TS