Self-Assessment Deadline January 2026: The Complete Director's Checklist

Key Dates You Cannot Miss

The 31 January deadline isn't a gentle suggestion. Here's what happens if you miss it.

31 January 2026 is the last day to file your self-assessment online AND make your full payment. Miss either one and penalties start immediately.

Real example: A £5,000 tax bill paid 6 months late costs you £600 in penalties plus £219 in interest. That's nearly £820 extra just because you procrastinated.

Do You Actually Need to File?

Not every director needs to file. Here's how to know.

You definitely need to file if:

• You received any dividend income (even £1)
• Your salary was over £12,570
• You had bank interest over £500
• You had rental income
• You made capital gains
• You're claiming any tax relief (pension contributions, trading losses, Gift Aid)

You might not need to file if:

• Salary under £12,570 was your only income, AND
• HMRC hasn't asked you to file

Most directors with companies have dividend income, which means most of you need to file. If you're unsure, file anyway. The downside of filing when you didn't strictly need to is zero. The downside of not filing when you should have is £100 minimum.

What to Include in Your Return

Directors often declare income in the wrong section, which flags their return for enquiry. Here's what goes where.

Warning: Dividend income in the employment section triggers enquiries. Income in the wrong tax year triggers enquiries. Just get it in the right place.

Documents to Gather Before You Start

Don't start your return until you have these.

From your company:

• P60 (salary and tax deducted)
• Dividend vouchers for each dividend paid
• P11D form (if applicable)

From your bank:

• Statements showing interest received
• Total interest for tax year (6 April 2024 to 5 April 2025)

From HMRC or previous records:

• SA302 (if under a Time to Pay arrangement)
• Previous year's return reference
• Pension contribution statements
• Gift Aid receipts

Pro tip: Most directors get stuck here because their accountant has the P60 and dividend vouchers but hasn't sent them yet. Email your accountant today if you haven't got them. Don't wait until 25 January.

Common Mistakes That Trigger HMRC Enquiries

These are the patterns that make HMRC's systems flag your return for manual review.

Dividend errors (most common):

• Claiming dividend income in the wrong tax year (the tax year is April to April, not January to December)
• Declaring dividends without matching dividend vouchers
• Missing small dividends (HMRC has records from your company)

Employment section errors:

• Salary figure doesn't match your P60
• Tax already paid doesn't match your P60

Missing income:

• Not declaring all bank accounts
• Forgetting about interest or premium bonds
• Other sources like rental or freelance income

The good news: most of these are just administrative. If you catch them, you can amend your return before filing. If HMRC catches them, you'll get an enquiry letter 6 to 12 months later, which is annoying and more expensive to fix.

Payment Options and Spreading the Cost

If you can't pay in full by 31 January, you have options. The key is doing something before the deadline, not after.

Pay in full by 31 January: Cleanest option. No interest, no penalties, no stress.

Time to Pay arrangement: Ring HMRC Self Assessment on 0300 200 3310 and ask for a Time to Pay arrangement before 31 January. They'll negotiate a payment plan, usually 3 to 6 monthly instalments. You'll pay interest, but you won't get a late payment penalty. Most directors don't know this option exists.

Budget Payment Plan: If this is a recurring problem, set up automatic payments throughout the tax year. Less stressful than one lump sum in January.

Coding out: For smaller amounts (up to about £3,000), HMRC can adjust your PAYE coding in the next tax year to recover it gradually.

Don't ignore it: The worst thing you can do is neither pay nor arrange Time to Pay. You'll get a penalty automatically.

What to Do If You Can't File in Time

Filing late costs money. But the hierarchy is clear: file late is better than don't file at all, which is better than file late and don't pay.

If you're going to file late:

1. File anyway, as close to the deadline as possible. Even 1 day late is better than 1 week late.
2. Include a reasonable excuse letter explaining why (illness, bereavement, accountant delay). HMRC sometimes accepts these.
3. Pay what you owe as soon as possible.
4. Appeal within 30 days if you have a strong excuse for the delay.

Need professional help urgently? Most accountants have January rush protocols. Ring your accountant now if you think you'll need help. Don't wait until 25 January.

Tools to Help You Plan

Use our free Director Salary Calculator to work out your optimal salary and dividend mix for the current tax year.

If you're concerned about the dividend tax increase coming in April 2026, our guide explains how it affects your take-home pay and what you can do about it.