Every CIS monthly return must reach HMRC by the 19th of the month following the tax month it covers, and a single day's delay triggers an automatic £100 penalty [1]. A contractor who deducts tax from a subcontractor at the standard rate withholds 20%, rising to 30% for a subcontractor who cannot be verified, and every one of those payments must appear on the return [8]. For a contractor juggling several jobs, the monthly return is the most exacting recurring deadline in construction payroll.
The return itself is the CIS300, the form on which a contractor declares every subcontractor paid in the tax month, the gross payment, the cost of materials, and the tax deducted [11]. Filing it correctly is only part of the job: the contractor must also verify subcontractors first, issue deduction statements afterwards, and pay the withheld tax to HMRC on a separate deadline [5].
This guide walks through the process in order, from preparing the figures and verifying subcontractors to completing the CIS300, filing it, handling nil returns and inactivity, issuing deduction statements, paying HMRC, and correcting a return that has gone out wrong.
Key takeaways
- The CIS monthly return, form CIS300, must reach HMRC by the 19th of the month following the tax month.
- Subcontractors must be verified before payment, which sets the deduction rate at 20%, 30% or 0% for gross payment status.
- A contractor who paid no subcontractors must still file a nil return or set a period of inactivity for up to six months.
- Deductions are paid separately, by the 22nd if paid electronically or the 19th if paid by post.
- A payment and deduction statement must be given to each subcontractor within 14 days of the tax month end.
Step 1, understand what the return covers
A CIS monthly return covers a tax month, which runs from the 6th of one month to the 5th of the next, not a calendar month [1]. The return for the tax month of 6 May to 5 June, for example, reports every qualifying payment made in that window and must reach HMRC by 19 June [1]. The obligation sits with the contractor, and a contractor with an active CIS scheme is expected on the system every month, whether or not it paid anyone [9].
The return reports payments for construction work only. It captures the gross amount paid to each subcontractor, the direct cost of any materials the subcontractor supplied, and the tax deducted from the balance [2]. VAT is excluded from the figures reported, and the deduction is calculated on the labour element after materials are stripped out [2]. A contractor new to the scheme should read the broader mechanics of payroll for construction and CIS before its first return.
Step 2, verify subcontractors and set the deduction rate
Verification is the step that determines how much tax to withhold, and it happens before payment, not on the return. The contractor checks each subcontractor with HMRC, which confirms whether the subcontractor is registered and at what rate deductions should be taken [5]. The verification result drives the whole return, so getting it right first avoids correcting figures later.
The three deduction rates are fixed and depend on the subcontractor's status. The table below sets them out.
| Subcontractor status | Deduction rate | When it applies |
|---|---|---|
| Gross payment status | 0% | Subcontractor approved to be paid in full, settling tax at year end |
| Registered and verified | 20% | Standard rate for a matched, registered subcontractor |
| Unregistered or unmatched | 30% | Subcontractor not registered or not matched at verification |
The standard rate for a registered and verified subcontractor is 20% [8]. The higher rate of 30% applies where a subcontractor is not registered for CIS or cannot be matched during verification [8]. A subcontractor holding gross payment status is paid in full with no deduction and settles its own tax and National Insurance at the end of the year [5].
Confirming verification on the return
The CIS300 asks the contractor to confirm that verification has been done. The contractor puts a marker in the verification box to confirm that every subcontractor on the return, and on any continuation sheets, has been properly verified with HMRC or was already included in a previous monthly return in the current tax year [11]. A subcontractor paid in an earlier month of the same tax year does not need re-verifying, which is why the box refers to prior returns [2].
Step 3, complete the CIS300
With verification done and payments made, the contractor completes the return. For each subcontractor the CIS300 records the total payments made, excluding VAT, the cost of materials, and the amount deducted where a deduction was taken [11]. Where no deduction was made, because the subcontractor holds gross payment status, the deduction boxes are left at zero rather than filled in [11].
Two practical rules catch contractors out. First, the return must not contain negative values: where commercial CIS software produces an entry of less than zero, the contractor enters zero instead [11]. Second, the contractor must complete the monthly declarations on the return, including confirming that the employment status of each subcontractor has been considered and that none of the payments are for work that should have been treated as employment [2].
Handling more subcontractors than the form holds
The paper CIS300 holds a limited number of subcontractors, so larger contractors use continuation sheets. Where a contractor pays more subcontractors than the main form allows, it uses continuation sheets and can use as many as it needs [1]. HMRC issues a pre-printed continuation sheet, the CIS300(CS), with the return where its records show five or more subcontractors verified or paid previously, and a blank version, the CIS300(CS)(Man), is available for others [9]. Most contractors now avoid the paper form entirely by filing through software, which removes the sheet limit altogether [1].
Step 4, file the return by the 19th
The return can be filed through HMRC's free online CIS service or through commercial payroll software, and it must arrive by the 19th of the month following the tax month [1]. There is no weekend extension built into the rule, so contractors treat the 19th as a hard stop and file ahead of it where the date falls awkwardly [3]. Software filing carries the advantage that the return is validated before submission, which reduces the risk of a rejected or incomplete return [1].
Filing late carries an automatic penalty that escalates quickly, so the deadline matters more than almost any other in the scheme. The table below shows the penalty ladder.
| How late | Penalty |
|---|---|
| 1 day late | £100 fixed penalty |
| 2 months late | £200 fixed penalty |
| 6 months late | £300 or 5% of the deductions, whichever is higher |
| 12 months late | A further £300 or 5% of the deductions, rising to as much as £3,000 or 100% for the most serious cases |
A return even one day late attracts the £100 fixed penalty, and a second fixed penalty of £200 follows at two months [3]. At six months a further penalty of £300 or 5% of the deductions applies, and at twelve months another charge is added, which can reach £3,000 or 100% of the deductions in cases of deliberate and concealed failure [10]. Accountants running CIS for several clients often centralise the filing calendar so no scheme slips, a discipline that a multi-client payroll dashboard supports by tracking each client's deadline separately.
Step 5, handle nil returns and inactivity
A month with no subcontractor payments still needs action. Even where the contractor made no payments to subcontractors during the tax month, it must tell HMRC by making a nil declaration, and failing to do so exposes the contractor to a penalty [1]. The nil return is filed the same way and by the same deadline as an ordinary return [9].
Where a contractor expects a quiet spell, it can avoid a run of nil returns by requesting a period of inactivity. A contractor can ask for a period of inactivity to be set on its scheme record for the next six months, and once that is in place it no longer has to file a nil return for each of the months the period covers [4]. The contractor must resume filing as soon as it pays a subcontractor again, even if the inactivity period has not yet expired [4].
Step 6, issue payment and deduction statements
The return is not the only document the contractor must produce. Where the contractor makes a deduction, it must give the subcontractor a payment and deduction statement within 14 days of the end of the tax month [7]. For the tax month running 6 May to 5 June, the statement must reach the subcontractor by 19 June, the same date as the return [5].
The statement is the subcontractor's evidence of the tax already withheld, and it feeds directly into how the subcontractor recovers that tax later. Each statement shows the gross payment, the cost of materials, and the amount deducted [7]. A limited company subcontractor uses these statements to reclaim its CIS deductions through the payroll scheme, while a sole trader sets them against the tax due on its self-assessment return [12]. Contractors that also run PAYE find it simpler to produce statements from the same records, which is why many use integrated payroll software for SMEs rather than a standalone CIS tool.
How the subcontractor uses the statement
The deduction statement is not a formality: it is the document a subcontractor relies on to avoid paying tax twice. A limited company subcontractor offsets the CIS deductions shown on its statements against the PAYE, National Insurance and other amounts it owes as an employer, reporting the total on its Employer Payment Summary each month [12]. Where the deductions exceed what the company owes, it can carry the excess forward or reclaim it from HMRC at the year end [12].
A sole-trader subcontractor takes a different route, setting the deductions against the income tax and National Insurance due on its self-assessment return [2]. In both cases the contractor's accuracy on the statement directly affects the subcontractor's cash position, which is why the 14-day deadline is treated as firm rather than flexible [7]. The full penalty ladder and payment mechanics are set out in the companion guide to CIS returns and deadlines.
Step 7, pay the deductions to HMRC
Filing the return and paying the money over are two separate obligations with two different deadlines, and confusing them is a common cause of interest charges. The deductions are paid to HMRC together with PAYE tax and National Insurance, by the 22nd of the month where payment is made electronically, or by the 19th where payment is made by post [6]. Where the 22nd falls on a weekend or bank holiday, cleared payment must reach HMRC by the previous banking day [6].
Paying late carries its own consequences, separate from the return penalties. A contractor that pays deductions late may be charged interest and penalties on the unpaid amount [6]. Contractors that pay monthly should note that the same 22nd deadline governs PAYE, so aligning the two payments in a single monthly routine reduces the risk of missing either [5].
Step 8, correct a return that has gone out wrong
Mistakes on a filed return can be corrected, within limits. A contractor can amend a CIS return for the current tax year and the previous tax year, which covers the common cases of a wrong figure or a subcontractor left off [1]. Amendments are made through the same channel as the original filing, and correcting an error promptly is preferable to leaving it for HMRC to find [2].
Where a penalty has been issued that the contractor believes is wrong, there is a route to challenge it. The contractor normally has 30 days to appeal a penalty, either online or in writing, setting out the reason the penalty should not apply [3]. A reasonable excuse, accepted by HMRC, can lead to a penalty being cancelled, but the appeal must be made within the time limit [10]. Platforms that embed UK payroll through an HMRC-recognised payroll API can flag a missing or inconsistent return before the deadline, which is the cheapest form of correction of all.
Conclusion
The CIS monthly return rewards routine over rescue. A contractor that verifies subcontractors before paying them, files the CIS300 ahead of the 19th, issues deduction statements on time, and pays HMRC by the 22nd rarely meets a penalty, because each step feeds cleanly into the next. The trouble almost always comes from treating the return as a single monthly event rather than the end of a chain that starts at verification.
As construction records move from paper to software, the contractors that cope best are those whose CIS, PAYE and payment records sit together, so a figure entered once flows through the return, the statement and the payment without being rekeyed. That single source of truth is what turns the monthly return from a deadline to dread into a step that closes itself.
FAQs
What is the difference between the CIS return deadline and the payment deadline?
They are two separate obligations. The CIS monthly return, the CIS300, must reach HMRC by the 19th of the month following the tax month. The deductions themselves are paid to HMRC by the 22nd if paying electronically, or the 19th if paying by post. Filing the return on time does not settle the money owed, and paying on time does not file the return, so a contractor must do both.
Do I need to file a CIS return if I paid no subcontractors?
Yes, unless a period of inactivity is in place. A contractor with an active CIS scheme that made no payments in a tax month must still file a nil return, and failing to do so can trigger a penalty. To avoid a run of nil returns during a quiet spell, a contractor can ask HMRC to set a period of inactivity of up to six months, after which it must resume filing when it next pays a subcontractor.
When must I give a subcontractor their deduction statement?
Within 14 days of the end of the tax month. For the tax month running 6 May to 5 June, the payment and deduction statement must reach the subcontractor by 19 June. The statement shows the gross payment, the cost of materials, and the tax deducted, and the subcontractor needs it to reclaim or account for the tax later.
Can I amend a CIS monthly return after filing it?
Yes. A contractor can amend a CIS return for the current tax year and the previous tax year, which covers most corrections such as a wrong figure or a subcontractor omitted in error. Amendments are made through the same online service or software used for the original return. Correcting an error promptly is better than leaving it, because an uncorrected return can attract penalties if HMRC identifies the mistake first.
