31 January 2027 Checklist for CIS Subcontractors

The short version

Your 2025/26 online return and any tax you owe are due by 11:59pm on 31 January 2027, which is a Sunday.
You need your contractors' payment and deduction statements. On the return, your turnover is the gross amount before CIS, and the CIS taken is entered as deductions.
If CIS has taken more than your tax bill, HMRC pays the difference back. You can file any time from 6 April 2026.
30 December 2026 only matters if you have PAYE income and owe under £3,000. Most CIS-only subcontractors pay by 31 January.
Earlier years: the usual four-year limit puts 2022/23 at 5 April 2027 and the 2024/25 online amendment window at 31 January 2027.

The dates that matter

Date	What it is for
30 December 2026	Last day to file online if you want an underpayment under £3,000 collected through your PAYE tax code. Needs PAYE income.
Friday 29 January 2027	Safe payment date. 31 January is a Sunday and some payment methods take longer to reach HMRC over a weekend, so pay by the Friday if you can.
31 January 2027	Online 2025/26 return and payment of any tax owed, including the first payment on account for 2026/27 if one is due.
31 January 2027	Usual last day to correct your 2024/25 return online.
5 April 2027	Usual four-year limit for a 2022/23 claim (see the last section, because we word this one carefully).

Gather your papers

Your UTR and Government Gateway login. Registering again takes time, and HMRC posts some codes, so do not leave this to the last week.
Your payment and deduction statements. These are the monthly statements your contractors give you. Chase any that are missing now. The CIS records guide shows what to keep.
Your total income before CIS. Add up your gross invoices, then check them against your bank statements.
Your costs. Tools, van, mileage, insurance and phone, kept with receipts. The mileage guide helps you pick the better van method.
Your CIS total. Add up the CIS shown on your statements. You can also see what contractors have reported to HMRC in your online account.

Fill in the return

In the self-employment section of your Self Assessment return you enter your turnover (the gross amount before CIS was taken off), your allowable expenses and the total CIS deductions. HMRC treats CIS deductions as tax you have already paid, so the return sets them against your bill.

If CIS has taken more than your bill, HMRC repays the difference.
If you still owe tax, you pay it by 31 January.
If you are owed money, include your bank details so a refund can be paid straight in.

CIS Tax & Refund Calculator

Run your figures first: enter your pay, materials and costs to see your likely bill or refund before you open the return.

Open the calculator

Pay what you owe

Work out the amount before you file, so January is not a surprise. Our CIS refund guide has a worked example. If you are not owed a refund, put money aside with the tax set-aside calculator.

If your bill is £1,000 or more, you may also have to make payments on account for the next year, the first on 31 January and the second on 31 July. GOV.UK says you do not have to if last year's bill was under £1,000, or if you paid more than 80% of it outside Self Assessment. CIS deductions often reduce what is left, so check the payments on account guide or the calculator before you pay.

Do not file late

A late return costs a £100 penalty even if you owe nothing, and further penalties follow at 3, 6 and 12 months. Paying late adds interest and 5% penalties at 30 days, 6 months and 12 months. The details are in our Self Assessment deadlines guide. If you cannot pay in full, contact HMRC before the deadline.

Earlier years

If you think CIS has taken too much in an earlier year, there are two dates to keep in mind.

2024/25: amend by 31 January 2027. GOV.UK says you can correct a return within 12 months of the Self Assessment deadline, and gives 31 January 2027 as the example date for 2024/25. HMRC's Self Assessment Claims Manual also says overpayment relief does not apply where the mistake relates to CIS deductions, so if you left deductions off a 2024/25 return, use the amendment window while it is open.

2022/23 and older: the four-year limit. For individuals, HMRC's manuals give a general four-year time limit for claims and for a late return to create a Self Assessment, counted from the end of the tax year. For 2022/23 the tax year ended on 5 April 2023, so the usual limit is 5 April 2027. The CIS pages on GOV.UK do not state this limit directly, so please treat the date as the usual rule rather than a guarantee, and contact HMRC if you are near it.

A return for 2022/23 was due on 31 January 2024, so a late return may also bring late filing penalties. The CIS refund guide explains how to claim for earlier years.

After you file

Keep a copy of the return and your statements.
Set up your payments on account plan if one is due on 31 July.
If you are in Making Tax Digital for Income Tax, remember your quarterly updates as well. The 7 November 2026 update guide covers the next one.
Add the dates to your phone with the free HMRC dates calendar.

Questions people ask

When is the Self Assessment deadline for CIS subcontractors?

Subcontractors file like any other self-employed person. For the 2025/26 tax year, an online return is due by 11:59pm on 31 January 2027, and the tax you owe must be paid by the same time. A paper return was due by 31 October 2026.

Do I still have to file if CIS has already taken my tax?

If HMRC has asked you for a return, yes. The CIS deductions go on the return and are set against your bill. If CIS has taken more than your bill, you are due a refund. A late return can still get a £100 penalty even if you owe nothing.

Can I pay my bill through my tax code?

Only if you owe less than £3,000, already pay tax through PAYE (for example from a job or company pension) and file online by 30 December 2026. If CIS is your only income, you will normally pay by 31 January instead.

Where do I put my CIS deductions on the return?

In the self-employment section you enter your total turnover (the gross amount before CIS was taken off) and, separately, the total CIS deductions. Your monthly payment and deduction statements give you the totals.

I forgot to claim CIS tax on an earlier year. Is it too late?

Not necessarily. HMRC's manuals give a general four-year limit for claims by individuals, counted from the end of the tax year, which would make 5 April 2027 the usual last date for 2022/23. We could not find that CIS limit set out on GOV.UK itself, so treat it as the usual rule, not a promise, and contact HMRC if you are close to it.

Can I change my 2024/25 return?

You can correct a return within 12 months of the Self Assessment deadline, so GOV.UK says that for 2024/25 you will usually need to change it by 31 January 2027. After that you need to write to HMRC.

Is overpayment relief available if I missed CIS deductions?

HMRC's Self Assessment Claims Manual says overpayment relief does not apply where the mistake relates to the CIS deductions. That is a good reason to amend a return while the 12-month window is still open.

Sources

Checked against GOV.UK on 1 November 2026. Rates and rules change, usually from 6 April, so we re-check every guide at least once a year.