Self-Assessment: key dates and penalties

Failure to notify chargeability to tax, submit your Self-Assessment tax return on time, or pay tax when it is due can result in automatic penalties and interest. These charges can increase quickly the longer a return or payment is delayed, even where only a small amount of tax is involved.

Outlined below are the key Self-Assessment deadlines over the next year, together with an explanation of the penalties that apply if deadlines are missed. Understanding these dates is essential to avoid unnecessary costs and stress.

31 January 2026

A critical deadline for most taxpayers

This is one of the most important dates in the Self-Assessment calendar.

By 31 January 2026, the following must be completed:

• Online filing deadline for 2024/25 Self-Assessment tax returns
• Deadline for making certain claims and elections for the 2024/25 tax year
• Payment deadline for:
• • The balancing payment for 2024/25; and
  • The first payment on account for 2025/26 (where applicable)

Penalties for missing the filing deadline

• A fixed £100 late filing penalty applies immediately if your return is not submitted by 31 January 2026
• This penalty applies even if no tax is due or the tax has already been paid
• For partnerships, a £100 penalty per partner applies for a late partnership return

Paper returns

Paper returns for 2024/25 should normally have been filed by 31 October 2025. If they are not filed by 31 January 2026:

• They will be three months late
• HMRC may begin charging daily penalties of £10 per day, for up to 90 days
• This can result in penalties of up to £900

3 March 2026

First late payment penalty

If any 2024/25 tax remains unpaid, HMRC will charge the first automatic late payment penalty:

• 5% of the outstanding tax will be added to your liability

Interest will also continue to accrue on the unpaid amount until it is settled.

5 April 2026

Final deadline for older claims

This date marks the end of the four-year time limit for making certain claims and elections relating to the 2021/22 tax year.

If you are considering:

• Loss relief claims
• Overpayment relief
• Certain elections or adjustments

these must be made by 5 April 2026, or the opportunity will be lost permanently.

30 April 2026

Escalating penalties for late returns

By this point, penalties increase significantly.

Paper returns for 2024/25

If a paper return is still outstanding:

• It will now be six months late
• A further penalty may apply of:
• • 5% of the tax due, or
  • £300, if greater

Online returns for 2024/25

Online returns not filed by 30 April 2026 will be:

• Three months late
• Exposed to daily penalties of £10 per day, for up to 90 days
• This can result in additional penalties of up to £900

31 July 2026

Another key payment and penalty date

By 31 July 2026, the following apply:

• Second payment on account for 2025/26 is due (where applicable)

Late filing penalties increase again

If an online 2024/25 return is still outstanding:

• It will now be six months late
• A further penalty may be charged of:
• • 5% of the tax due, or
  • £300, if greater

1 August 2026

Second late payment penalty

If any 2024/25 tax remains unpaid, a second automatic late payment penalty will apply:

• A further 5% of the outstanding tax is charged

At this stage, a taxpayer could be facing:

• Two 5% late payment penalties
• Ongoing interest
• Multiple late filing penalties

even before the tax year is a full year late.

5 October 2026

Deadline to notify chargeability for 2025/26

If you have not received a tax return or notice to file from HMRC but you have:

• Income tax to pay; or
• Capital Gains Tax to pay

for the 2025/26 tax year, you must notify HMRC of your chargeability to tax by 5 October 2026.

Failing to do so can result in penalties for failure to notify, which are separate from late filing penalties.

31 October 2026

Paper return deadline for 2025/26

This is the deadline for submitting paper Self-Assessment returns for the 2025/26 tax year.

If your paper return is filed by this date, HMRC should be able to:

• Calculate your tax for you
• Notify you of the amount due by 31 January 2027
• Collect tax through your PAYE tax code, where the amount owed is less than £3,000

If a paper return is submitted after 31 October 2026:

• An automatic £100 late filing penalty will apply

Older returns

Paper returns for 2024/25 not submitted by this date will now be:

• 12 months late
• Subject to a further penalty of:
• • 5% of the tax due, or
  • £300, if greater

30 December 2026

Last chance for tax code collection

This is the deadline for online filing of 2025/26 returns if you want HMRC to:

• Collect tax owed (up to £3,000) through your PAYE tax code

Returns filed after this date may still be submitted online but tax will need to be paid directly.

31 January 2027

Major filing and payment deadline

By 31 January 2027, the following must be completed:

• Online filing deadline for 2025/26 tax returns
• Payment deadline for:
• • The balancing payment for 2025/26; and
  • The first payment on account for 2026/27 (where applicable)

Failure to meet this deadline will trigger the same cycle of late filing penalties, late payment penalties and interest as outlined above.

Time-to-Pay (TTP) arrangements

If you are struggling to pay your tax on time, you may be able to set up a Time-to-Pay (TTP) arrangement with HMRC.

A TTP allows you to:

• Pay your tax in instalments
• Avoid late payment penalties, provided the arrangement is agreed before the tax becomes overdue
• Reduce financial pressure while staying compliant

TTP arrangements are usually easier to obtain before the due date, so early action is essential.

How we can help

Please contact us if:

• You are unsure which deadlines apply to you
• You are concerned about meeting a filing or payment date
• You need help setting up a Time-to-Pay arrangement

We can guide you through the process, liaise with HMRC where appropriate, and help you avoid unnecessary penalties and interest. Book a 30 minute meeting now