Self Assessment Tax Return Deadlines: A Simple Guide

Who has to file a return

You need to complete a self assessment return if you were self-employed as a sole trader and earned above the trading allowance, if you were a partner in a business partnership, or if you have untaxed income that HMRC cannot collect through PAYE.

That second category is broader than people expect. Rental income, dividends above the allowance, savings interest, income from a side business, capital gains on property or shares, and foreign income all commonly trigger a filing requirement. So does the High Income Child Benefit Charge.

• Self-employed income above the trading allowance
• Partnership profits
• Rental or property income
• Dividends and savings interest above the allowances
• Capital gains on assets sold during the year
• Income from abroad, or non-UK residence with UK income

The dates that matter

The UK tax year runs from 6 April to 5 April. Everything else hangs off that.

What a late return actually costs

The penalty regime is automatic and largely non-negotiable. Missing the filing date by a single day triggers a £100 penalty even if you owe no tax at all.

After three months, daily penalties of £10 start accruing for up to 90 days. At six months and again at twelve months, further penalties of 5% of the tax due or £300 apply, whichever is greater. Late payment carries its own separate penalties at 30 days, six months and twelve months, plus interest running from the due date.

• 1 day late: £100 fixed penalty
• 3 months late: £10 per day, up to £900
• 6 months late: a further 5% of tax due or £300
• 12 months late: another 5% or £300, and potentially more in serious cases
• Late payment: 5% surcharges at 30 days, 6 months and 12 months, plus interest

Get your records ready early

The return itself rarely takes long. Assembling the underlying information is what consumes the time, and that is the part you can do in October rather than January.

• Income records: invoices, dividend vouchers, rental statements, interest certificates
• P60, P45 and P11D for any employment during the year
• Allowable business expenses with supporting receipts
• Pension contributions and gift aid donations
• Details of any assets sold and their original cost
• Your UTR and Government Gateway login details

Common mistakes worth avoiding

Most amendments we see trace back to a small number of recurring errors: forgetting to claim allowable expenses, omitting pension contributions or gift aid that would have extended the basic rate band, missing an income source entirely, and misunderstanding what payments on account represent.

The other frequent problem is treating the deadline as the target. Filing in January leaves no room to find the missing paperwork, no time to query an unexpected figure and no opportunity to plan for the payment. Filing in the autumn gives you months of notice on the bill.

Support for Derby businesses

Our tax accountants in Derby handle self assessment for sole traders, landlords, company directors and higher-rate taxpayers across Derbyshire, and the pattern is always the same: the clients who file early pay less, worry less and never see a penalty.

Pairing your return with ongoing bookkeeping removes the annual scramble altogether. When records are reconciled monthly, preparing the return becomes a review rather than a reconstruction, and there is time to plan around the bill before it lands.

If you are already late

File anyway, and file now. Penalties escalate with time, so the cost of a late return grows every month it sits unsubmitted. If you cannot pay the tax, submit the return first and then contact HMRC about a Time to Pay arrangement. They are considerably more accommodating with people who have filed than with those who have not.