Free tool
CIS deduction calculator
CIS is deducted from the labour element of a payment only, at 0%, 20% or 30% depending on the subcontractor’s verified status with HMRC, and the payment belongs to a tax month running from the 6th to the 5th rather than to a calendar month. This calculator applies all three rules and shows the whole build-up, so you can see what the deduction was taken from rather than only what it came to.
Last reviewed by Estimark. This page states periods and rates set by statute or by standard contract terms. Those move, and this date is when somebody last read the page against its source rather than the day the site was built.
CIS deduction
Work out the deduction on a payment
Nothing is sent anywhere and nothing is stored. The arithmetic runs in your browser.
The gross figure on the subcontractor's invoice.
Decides which tax month it belongs to, and when the return is due.
Deduct from this payment
£140.00
20% of £700.00 labour
- Total payment
- £1,000.00
- Less excluded
- − £300.00
- Labour, the deduction base
- £700.00
- Deduction rate
- 20%
- CIS deducted
- − £140.00
- Pay the subcontractor
- £860.00
CIS tax month 6
6 Sept 2026 to 5 Oct 2026
The CIS300 covering it is due by 19 Oct 2026. A tax month runs from the 6th to the 5th, so a payment early in a calendar month usually belongs to the period before it.
Rounding follows HMRC: stated amounts to the nearest penny, the deduction itself down. Estimark applies the same arithmetic on every payment and records the CIS300 with both statutory declarations. How CIS works in Estimark.
What is CIS deducted from?
Labour only. The deduction base is the total payment less materials, less VAT, less plant hire, and less other allowable exclusions such as the CITB levy and fuel.
- Everything excluded is still paid to the subcontractor in full. It comes off the base the percentage applies to, not off the payment.
- Taking 20% off the whole invoice under-pays the subcontractor on every job that includes materials, and over-pays HMRC.
- The base is floored at zero, so exclusions larger than the payment produce no deduction rather than a negative one.
The figures come from what the subcontractor has stated. No calculator can read an invoice and decide which part of it was materials.
What rate applies?
One of three, decided by the subcontractor’s verified status with HMRC.
- An unverified subcontractor is 30% regardless of what status is recorded against them. That is what verification is for.
- Verifying is the contractor’s duty, and getting the rate wrong is a penalty matter for the contractor rather than the subcontractor.
| Status | Rate |
|---|---|
| Verified for gross payment status | 0% |
| Verified and registered | 20% |
| Unverified, unmatched or higher rate | 30% |
Which tax month does a payment belong to?
A CIS tax month runs from the 6th of one month to the 5th of the next, so the answer is often not the calendar month the payment was made in.
- A payment dated 3 May belongs to the period that began on 6 April, which is tax month 1.
- Tax month 1 is 6 April to 5 May. The tax year is named for the year it starts.
- The CIS300 covering a period is due by the 19th of the month that period ends in.
Filing late is a fixed penalty that starts at £100 and escalates, so the date matters as much as the figure.
How is it rounded?
Stated amounts to the nearest penny, and the deduction itself down, which is the direction HMRC takes.
- Rounding down cannot under-deduct against the exact figure, and under-deducting is the direction HMRC charges interest on.
- This calculator works in whole pence from the digits you type, so a half-penny figure is rounded rather than quietly lost.
Common questions
- Is CIS deducted on materials?
- No. CIS is deducted from the labour element only. Materials, VAT, plant hire and other allowable costs such as the CITB levy and fuel are removed from the base before the percentage is applied, and are still paid to the subcontractor in full.
- What is the CIS rate for an unverified subcontractor?
- 30%. The higher rate applies to anyone not verified with HMRC, or whose details HMRC could not match, whatever status is recorded against them locally. Verifying the subcontractor is the contractor’s responsibility.
- When does a CIS tax month start and end?
- A CIS tax month runs from the 6th of one month to the 5th of the next. Tax month 1 is 6 April to 5 May. A payment dated 3 May therefore belongs to tax month 1, not to May.
- When is the CIS300 due?
- By the 19th of the month in which the tax period ends. The return covering 6 April to 5 May is due on 19 May. Filing late incurs a fixed penalty starting at £100.
- Does this calculator store anything?
- No. The arithmetic runs in your browser. Nothing is sent to a server, nothing is stored, and there is no email address to give.
CIS compliance in Estimark
Labour-only deduction, HMRC verification, and the CIS300 recorded with its declarations.
ReadHow CIS deductions are calculated
The deduction base, the three rates, and what comes off before the percentage.
ReadCIS tax months explained
Why a payment on the 3rd belongs to the period that started on the 6th before it.
ReadFor sole traders
Quote and invoice from the phone, with CIS and the reverse charge handled.
Read