Invoicer → CIS calculator
CIS tax calculator
Two calculators for UK construction subcontractors. The first works out what a contractor should deduct from a payment. The second estimates the refund you're owed at the end of the year — which, for most subbies on the 20% rate, is a lot more than they expect.
1. Deduction on a single payment
What the contractor should withhold, and what actually lands in your bank.
- Invoice total (ex VAT)
- —
- Materials — not deductible
- —
- Deduction on labour
- —
- You get paid
- —
2. Annual refund estimate
Take these figures from your payment and deduction statements and your records for the whole tax year.
- Profit (turnover − expenses)
- —
- Personal allowance
- —
- Income tax
- —
- Class 4 National Insurance
- —
- Total due for the year
- —
- Already deducted under CIS
- —
- Refund due
- —
Rates and thresholds used in this calculator
These are the standard UK figures for a sole trader. Thresholds have been frozen for several years but are set by government and do change — check the current position on GOV.UK before you rely on the result.
| Personal allowance | £12,570 |
| Basic rate — 20% | on the first £37,700 taxable |
| Higher rate — 40% | above £50,270 income |
| Additional rate — 45% | above £125,140 income |
| Personal allowance taper | £1 lost per £2 over £100,000 |
| Class 4 NI — 6% | £12,570 to £50,270 profit |
| Class 4 NI — 2% | above £50,270 profit |
Class 2 National Insurance is not charged where profits are above the small profits threshold, so it isn't included. Student loan repayments, the High Income Child Benefit Charge, other employment income and payments on account are not modelled.
Invoicing as a subcontractor?
Split labour and materials properly so the deduction is taken on the right figure.
Create your invoice free →How the CIS deduction actually works
Under the Construction Industry Scheme, a contractor paying a subcontractor has to withhold a slice of the payment and send it to HMRC on your behalf. It isn't a tax in its own right — it's an advance payment against the income tax and National Insurance you'll owe at the end of the year.
Three rates apply, and which one you get depends entirely on your registration status:
| Rate | When it applies |
|---|---|
| 0% | You hold gross payment status. You're paid in full and settle the whole bill through Self Assessment. You have to apply and meet turnover, compliance and business tests. |
| 20% | You're registered under CIS and the contractor has verified you with HMRC. This is the standard position for most subcontractors. |
| 30% | You're not registered, or the contractor tried to verify you and couldn't. An expensive way to find out your details don't match HMRC's records. |
What the deduction is taken from
This is where money gets lost. The deduction applies to the labour element only. Before the percentage is applied, the contractor should strip out:
- Materials you paid for and are recharging, at cost.
- Plant hire you hired in, and fuel for that plant.
- Consumable stores genuinely used up on the job.
- Manufactured or prefabricated materials.
- VAT, which sits outside the calculation entirely.
If you own the plant rather than hiring it, the position is different — you can't deduct hire you didn't pay. And you can only take off what the materials genuinely cost you; you can't inflate the materials line to shrink the deduction, which HMRC does look at.
VAT and the reverse charge
If you're VAT registered and working for another VAT-registered business in the construction chain, the domestic reverse charge usually means you don't add VAT to the invoice — the customer accounts for it instead. You still show what the VAT would have been and state that the reverse charge applies. CIS is calculated on the net figures either way, which is why every box above says "excluding VAT".
Why you're probably owed money
The 20% comes off every payment from pound one. It takes no account of two things that massively reduce your real bill:
- Your personal allowance. The first £12,570 of income is normally tax-free — but CIS was deducted from it anyway.
- Your expenses. Tools, materials, van costs, fuel, insurance, protective clothing, phone, accountancy fees. You're taxed on profit, not turnover, and CIS ignored all of it.
Put those together and the arithmetic is stark. Run the numbers in calculator 2 above: a subbie turning over £45,000 with £9,000 of expenses has £7,200 deducted, but a real liability nowhere near that. The gap is your money, sitting with HMRC until you claim it.
You claim it by filing your Self Assessment return after the tax year ends on 5 April. You can file from 6 April. Most people wait until January, which means waiting nine extra months for a refund they could have had in April.
Common questions
How much is CIS deducted at?
20% if you're registered and verified, 30% if you're not registered or can't be verified, and 0% with gross payment status.
Is CIS deducted from materials?
No — labour only. Materials, plant hire, fuel for plant, consumable stores and VAT all come off before the percentage is applied. Itemise them on your invoice or you risk the deduction being taken on the lot.
Why do CIS subcontractors usually get a refund?
Because 20% is taken from every payment without any regard for your personal allowance or your expenses. Your actual bill is calculated on profit after both, so it's normally much lower than the total deducted.
When can I claim my CIS refund back?
After 5 April, through your Self Assessment return. You can file from 6 April — filing early gets the refund processed sooner rather than waiting for the January deadline.
Do I still need to file a return if CIS was deducted?
Yes. CIS deductions are payments on account, not a final settlement. Without a return HMRC can't work out what you actually owe or repay the difference.
What if I'm a limited company rather than a sole trader?
The mechanics differ — deductions are set against your company's PAYE and NI liabilities through the monthly payroll process, rather than against a personal Self Assessment bill. This calculator models the sole trader position only.
What do I need to keep to claim it back?
Your payment and deduction statements from every contractor, plus your invoices and expense receipts. HMRC can ask you to evidence the figures.
Would you use this as an app?
I'm considering building a proper CIS tracker — log every statement through the year, see the running refund, export it for your accountant. If that'd be useful, tell me what you'd want in it.
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