Paying Self Assessment Through Your Tax Code

You can pay a Self Assessment bill through your tax code if you owe less than £3,000, already pay tax through PAYE on wages or a pension, and file your return online by 30 December (or on paper by 31 October). HMRC then collects the tax in small amounts from your pay over the next tax year instead of you paying a lump sum by 31 January. This guide explains how paying Self Assessment through your tax code works, who qualifies, and when it makes sense.

Key takeaways

• Coding out is available if you owe less than £3,000 and have PAYE income.
• For 2025/26 returns, file online by 30 December 2026 to use it.
• The tax is collected through your wages or pension during 2027/28.
• You can opt out on your return and pay directly instead.
• Missing 30 December is fine, but you then pay by 31 January 2027.

What does "paying through your tax code" mean?

Your tax code tells your employer or pension provider how much tax-free pay to give you before deducting Income Tax. When HMRC "codes out" a Self Assessment debt, it reduces your tax code for the following tax year so that a little more tax is taken each payday. Over the year, those small extra deductions add up to the amount you owed. You do not make a separate payment to HMRC for that amount. GOV.UK explains the rules on its page about paying through your tax code.

Who qualifies

According to GOV.UK, HMRC collects what you owe through your tax code if:

• you owe less than £3,000 on your Self Assessment bill
• you already pay tax through PAYE, for example as an employee or on a workplace or private pension
• you submitted your paper return by 31 October or your online return by 30 December

HMRC also has limits on how much extra tax it will collect through a code relative to your PAYE income, so a debt is not always coded out even where the three conditions above are met. Check the current conditions on GOV.UK.

The people who most often use coding out are employees with a small side business, such as weekend delivery work, freelance design or a little rental income. If that is you, our guide to side income and Self Assessment explains when you need to file at all.

Coding out vs paying directly

For other ways to pay, see our guide to Self Assessment payment methods and deadlines.

How to pay through your tax code: step by step

1. Gather your figures early. P60 or pension statements, side income records, expense receipts and any interest or dividend figures.
2. Prepare the return in November or early December. This leaves room to fix login or calculation problems before 30 December.
3. Check the tax due. If the amount is under £3,000 and you have PAYE income, coding out may apply.
4. Leave the opt-out box alone if you want coding out. Tick it only if you would rather pay directly.
5. File online by 30 December. For paper returns, the date is 31 October, as covered in our paper return guide.
6. Watch for your new tax code. HMRC will issue a coding notice for the next tax year. Check the amount being collected matches your return.
7. Check your payslips from April. The extra tax should appear as slightly higher deductions each month.

Worked example (illustrative example)

Illustrative example only, not a real person. A full-time warehouse supervisor taxed through PAYE also does freelance photography at weekends. For 2025/26 the photography made a taxable profit of £4,000. Their salary already uses their Personal Allowance and keeps them within the basic rate band, so the profit is taxed at 20%, giving £800 of Income Tax. A self-employed profit this small is unlikely to attract Class 4 National Insurance, and the return will confirm the final figure.

The £800 is well under £3,000. They file online on 12 December 2026 and leave the opt-out box blank. HMRC adjusts their tax code for 2027/28, and from April 2027 roughly one-twelfth of the amount is collected from each monthly payslip. They make no lump-sum payment on 31 January 2027 for this amount. Had they filed on 15 January 2027 instead, the return would still be on time, but they would need to pay the whole balance directly by 31 January 2027.

When coding out may not suit you

• Your income changes a lot. If you change jobs or stop work, the adjusted code may not collect everything, and HMRC will then ask you to pay the rest.
• You prefer one clear payment. Some people find it easier to pay in January and keep their monthly pay predictable.
• You have payments on account. These have their own rules. Read our guide to payments on account and the GOV.UK guidance on payments on account.

Common mistakes

• Filing on 31 December or later and expecting coding out. The online date is 30 December.
• Ticking the opt-out box by accident. Read that section of the return carefully.
• Not checking the new tax code. Codes can be wrong. Compare the coding notice with your return.
• Forgetting a second employment or pension. HMRC may adjust the code on one source only, so check both.
• Assuming coding out reduces the tax. It changes when and how you pay, not how much you owe.

How we can help

We prepare Self Assessment returns for employees with side income, drivers, landlords and company directors, on a fixed fee from £180 per year. If you want to use coding out for your 2025/26 return, we need your information in good time to file before 30 December 2026. See our personal tax service, check our pricing, or contact us to get started.