Self Assessment Deadlines 2026/27 — Key Dates & Penalties

Self Assessment runs on a fixed calendar that catches thousands of people every year. For the 2026/27 tax year — 6 April 2026 to 5 April 2027 — the three dates that matter are 5 October 2027 (registration for first-time filers), 31 October 2027 (paper returns) and 31 January 2028 (online filing and payment). Miss the January deadline by a single day and a £100 penalty lands automatically, with daily penalties following after three months. Check your own dates with the Self Assessment Calculator→.

This guide maps the full deadline calendar, the payments on account system, and the penalty ladder so you never pay more than you owe.

Key Dates at a Glance

You can file online from the first day of the new tax year — 6 April 2027 for 2026/27 — so there is no reason to wait. HMRC's system handles the January surge badly, and filing early also means knowing your bill and planning payments months ahead.

Registration

First-time filers must normally tell HMRC by 5 October 2027 if they need to complete a return for 2026/27. Register on GOV.UK and follow the instructions for obtaining access to Self Assessment. Common reasons include self-employment gross income over £1,000, being a business partner, owing the High Income Child Benefit Charge outside PAYE, having taxable gains or untaxed income, or being an off-payroll worker with a student or postgraduate loan. This is not an exhaustive list: use HMRC’s eligibility checker if your circumstances are unusual.

Filing Deadlines and Penalties

Late payment penalties run separately: 5% of the unpaid tax at 30 days, a further 5% at 6 months, and another 5% at 12 months. Interest is charged on late payments at the applicable HMRC rate. There is no grace period for the £100 — but HMRC will consider cancelling it for a reasonable excuse such as serious illness or bereavement, supported by evidence. "I forgot" is not a reasonable excuse.

Payments on Account

If your 2026/27 bill (after tax deducted at source) is over £1,000 and less than 80% of the tax was deducted at source, you pay half of it on 31 January 2028 as an advance toward 2027/28, and the other half on 31 July 2028. A £1,800 bill therefore means paying £2,700 on 31 January (£1,800 plus £900 on account) and £900 on 31 July. If your income falls, you can apply to reduce the payments on account — but reductions that turn out too low attract interest.

How to Pay

Payments on account and balancing payments all flow through the same channels. If you cannot pay in full, use HMRC's current payment-plan service to check whether you are eligible for a Time to Pay arrangement. Eligibility, the route and the permitted duration depend on your circumstances. An acceptable arrangement made on or before a late-payment penalty trigger can prevent the penalties that would otherwise arise during the arrangement, but interest continues and late filing remains a separate issue.

Reasonable Excuse and How to Appeal

The £100 late-filing penalty is automatic, but HMRC will consider cancelling it where you had a reasonable excuse — something beyond your control that prevented filing on time. Serious illness with medical evidence, the death of a close relative, a fire or flood, or a failure of HMRC's own systems may qualify, depending on the facts. Forgetfulness, holidays and pressure of work do not normally qualify. Relying on an accountant does not automatically transfer responsibility: you remain responsible for the return, although HMRC assesses any reasonable-excuse explanation on its facts.

Appeal using the route and deadline shown on the penalty notice, normally through your HMRC account, and attach the evidence. If HMRC rejects the appeal you may be able to ask for an independent review or appeal to the tax tribunal, subject to the applicable process and time limits. The same reasonable-excuse route can apply to late-payment penalties, but an inability to pay is not automatically a reasonable excuse; contact HMRC promptly about a payment arrangement. Penalties that are upheld attract interest and, in some cases, can grow substantially — which is why the deadline, not the amount, is the part of Self Assessment you must never miss.

Time to Pay and Instalment Arrangements

If you cannot pay on 31 January, use HMRC's current payment-plan tool or contact HMRC promptly. Eligibility, payment-plan limits and duration depend on the debt and your circumstances. An acceptable arrangement made on or before a penalty trigger can avoid the relevant late-payment penalty during the arrangement, while interest continues. HMRC may ask for income-and-expenditure information before agreeing instalments, particularly where the online route is unavailable or the debt is more complex. Do not assume that an application alone stops penalties: confirm the arrangement and follow its terms.

Time to Pay does not stop the £100 late-filing penalty if the return itself is late, so the two must be handled separately — file the return by 31 January even if you cannot pay, then arrange the payment plan. If you genuinely expected a refund and the bill is a surprise, check your figures before agreeing anything: an amended return that reduces the liability can be filed within 12 months of the deadline, and HMRC recalculates the penalties and interest on the corrected amount.

Build a Deadline File, Not Just a Calendar Alert

Record the tax year, the date HMRC issued any notice, the registration date, the return type, the filing channel and the payment reference. A calendar reminder can tell you that 31 January is approaching, but it cannot prove that the return was submitted, the payment reached the correct HMRC account or an appeal was made within the notice period. Save the submission confirmation, payment receipt, bank reference and any HMRC message together.

Separate filing, payment and penalty dates in the schedule. Filing on time does not pay the bill, and a payment plan does not file the return. Payments on account also belong to the next tax year’s liability rather than being an extra tax charge for the previous year. If income has fallen, model a reduction request carefully from evidence of the expected liability; an overly low estimate can lead to interest on the shortfall.

Review the schedule when a new source of income appears, a trade starts or stops, a property is sold, a notice arrives or HMRC changes the account. Keep evidence for a reasonable-excuse appeal contemporaneously rather than reconstructing it months later. The exact route and deadline on the penalty notice take priority over a generic guide, so read the notice and current GOV.UK instructions before submitting an appeal or payment-plan request.

Frequently Asked Questions

Evidence and decision checks

A reliable self assessment deadlines 2026 27 review starts by fixing the tax year and the date on which the relevant event happened. Record the person's or business's status, the income or transaction category, the amount before tax, tax already withheld, and any election or claim being relied on. Do not combine a headline figure with a final liability: the result can change when another income source, a payment date, an ownership interest or a qualifying condition is added.

Keep the source documents behind every important input. Depending on the subject, that may include payslips, invoices, bank statements, contracts, provider statements, travel records, HMRC notices, payroll submissions, valuations or correspondence. Where an amount is apportioned, write down the method and retain the underlying total. If a correction is made, preserve the original figure and explain the reason, date and evidence for the replacement.

Before relying on the result, check the current official guidance for the same tax year and jurisdiction. Distinguish enacted law from a consultation, draft measure, announcement or future proposal, and record the effective date. Reconcile the final estimate to the relevant return, payroll record or HMRC account. A calculator or explanatory guide can support a decision, but it cannot replace the eligibility test or the official filing and payment process.

Plan your calendar with the Self Assessment Calculator→, then read the Self Assessment Filing Guide for the step-by-step return and the Payments on Account guide if your bill will exceed £1,000.

Official sources

• GOV.UK: Self Assessment tax returns — deadlines
• GOV.UK: Self Assessment tax returns — penalties
• GOV.UK: Who must send a tax return
• GOV.UK: Payments on account
• GOV.UK: Pay your Self Assessment tax bill
• HMRC: Self Assessment legal framework
• HMRC: Self Assessment manual