Self Assessment deadlines and payments on account

The Self Assessment dates that matter #

These are the deadlines for the return covering the tax year ended 5 April 2026, which is the one open now.

Two of these are quietly earlier than the famous 31 January. If you have never filed before, registration closes on 5 October 2026 and you cannot file without a UTR, which takes time to arrive. And if you want a small bill collected painlessly through next year's tax code instead of in one lump, the return has to be in by 30 December 2026, a month early.

What a payment on account actually is #

This is the single biggest shock in a first Self Assessment bill, and nothing on the return warns you about it beforehand.

When did payment on account start? It has been part of Self Assessment since the system began in 1996/97, so it is not new, just rarely explained. HMRC assumes that if you earned untaxed income last year you will earn something similar this year. So as well as paying last year's tax, you pay the same amount again in advance, split into two instalments of 50% each.

The good news, such as it is, is that this only bites once. In the second year the payments on account you already made come off the bill, and you are only settling the difference plus the next set of advances. It is the first January that hurts.

When you do not have to make payments on account #

There are two escapes, and you only need one of them.

• Your last bill was under £1,000.00. Small bills are simply settled in one go.
• More than 80% of your tax was already collected at source. If most of your tax came out through PAYE or was deducted before you were paid, HMRC is already holding the money and does not ask for advances.

That second one matters enormously in construction. A CIS subcontractor has 20% deducted from every payment before it reaches them, which often clears the 80% test on its own, and it is usually why a subcontractor is owed a refund rather than facing payments on account. You can estimate that with the CIS refund calculator.

Reducing your payments on account #

If you genuinely expect to earn less this year, you can apply to reduce the payments. The trap is what happens if you reduce them too far: HMRC charges interest on the shortfall from the original due date, not from the date you found out.

So reduce them on evidence, such as a contract ending or a business winding down, rather than on hope. An over-reduced payment on account is an expensive way to borrow money for six months.

Payment on account meaning, and getting one back #

The payment on account meaning in one line: an advance instalment towards a tax year that has not finished yet, based on what you owed for the year that has.

A payment on account refund arises when the advances turn out to be larger than the eventual bill, which happens whenever income falls. You do not claim it separately. Filing the return settles the year, the overpayment appears as a credit, and HMRC either repays it or sets it against the next instalment.

That is worth knowing if money is tight: filing early in the tax year, rather than waiting for January, is what releases an overpayment. A return sitting unfiled is a refund sitting unpaid.

Who has to file at all #

The Self Assessment criteria are broader than people assume, and being employed does not exempt you.

• Self-employed above the trading allowance
• Partners in a partnership
• Landlords with property income
• Company directors with income that is not fully taxed at source
• Anyone with untaxed savings interest, dividends or capital gains to report
• Anyone affected by the High Income Child Benefit Charge
• Anyone claiming certain reliefs, or with foreign income

Self Assessment corrections #

Filing something wrong is not a disaster, provided you fix it inside the window.

You can amend online through your Self Assessment account, though you have to wait 72 hours after filing before the option appears. The deadline is 12 months after the online filing deadline, so for the 2025/26 return you have until 31 January 2028. The amended bill shows immediately and any interest recalculates within a few days.

Past that deadline, you write to HMRC. To reclaim tax you overpaid, that is a claim for overpayment relief, available up to 4 years after the end of the tax year. To report income you left out, write and tell them: correcting it yourself attracts a far smaller penalty than being found out.

The Self Assessment address #

For anything that genuinely has to go by post:

Self Assessment, HM Revenue and Customs, BX9 1AS

That covers amended paper returns, overpayment relief claims and general correspondence. There is no street name and nothing is missing: BX9 is a special HMRC postcode that routes to their scanning operation. If you file online, nothing needs posting at all.

What late costs #

Filing and paying are separate obligations with separate consequences. The filing penalty starts at a fixed amount the day after the deadline and applies even when no tax is due, which is why a nil return still has to go in. Late payment attracts interest from the day after the due date, plus percentage-based penalties at longer intervals.

If you cannot pay, file anyway and then arrange Time to Pay. Filing on time removes one penalty entirely and costs nothing.

Payments on account, and working out what to pay #

Self assessment payment on account is the part that catches first-time filers. Where your bill is £1,000 or more and less than 80% was collected at source, HMRC asks for two advance payments towards next year, each half of this year's bill, due 31 January and 31 July.

That means the first January after you start can carry one and a half years of tax at once: the balancing payment for the year just filed, plus the first payment on account for the next. Budgeting for the headline figure alone is the most common cash flow mistake in Self Assessment.

There is no single self assessment tax calculator that replaces the return, because the figure depends on every source of income together. The sole trader calculator and the dividend tax calculator cover the two biggest components for most people filing a self assessment tax return UK wide.

Self assessment tax return forms are largely gone: filing is online through your HMRC account, and self assessment gov uk pages are the route in. Paper returns exist but carry an earlier deadline.

Common questions #

What is a payment on account?

It is an advance payment towards next year's tax bill. HMRC assumes you will earn roughly the same again, so it asks for the same tax again in two instalments. Each one is half of last year's bill, due 31 January 2027 and 31 July 2027.

When do I not have to make payments on account?

In two cases. If last year's Self Assessment bill was under £1,000, or if more than 80% of the tax you owed last year was already collected at source, through PAYE or deducted by a bank.

What are the Self Assessment dates for the 2025/26 return?

Register by 5 October 2026 if you have not filed before. A paper return is due 31 October 2026. An online return and the tax itself are both due 31 January 2027. The second payment on account follows on 31 July 2027.

Who has to file a Self Assessment return?

Mainly the self-employed above the trading allowance, company directors with untaxed income, landlords, partners in a partnership, people with untaxed savings, dividends or capital gains, anyone affected by the High Income Child Benefit Charge, and anyone HMRC has issued a notice to file to. A notice to file creates the obligation regardless of whether you owe anything.

How do I correct a Self Assessment return?

Online, through your Self Assessment account, at least 72 hours after filing. The deadline is 12 months after the online filing deadline, so for the 2025/26 return you have until 31 January 2028. After that you have to write to HMRC instead.

What is the Self Assessment address?

Self Assessment, HM Revenue and Customs, BX9 1AS. That address covers most Self Assessment post, including amended paper returns and letters about overpayment relief. Nothing about a return needs to be posted if you file online.

Can I reduce my payments on account?

Yes, if you genuinely expect to owe less than last year. You can apply to reduce them, but if you reduce them too far HMRC charges interest on the shortfall from the original due date. Reduce them on evidence, not on optimism.