CIS tax calculator (2025/26)
A free CIS tax calculator that estimates your Self Assessment bill and your likely refund from three numbers you already know. Most subbies overpay all year, find out what HMRC owes you.
- CIS already deducted–
- Taxable profit–
- Income tax due–
- Class 4 NI due–
Estimate only, absolutely not tax advice. Uses 2025/26 rates for England, Wales and NI (personal allowance £12,570, basic rate 20% to £50,270, higher 40%, Class 4 NI at 6% and 2%). Scottish bands differ. Payments on account, student loans and other income aren't included. Your accountant has the final word.
How CIS tax and refunds actually work
Under the Construction Industry Scheme, contractors take tax off your labour payments before the money ever reaches you: 20% if you're a verified subcontractor, 30% if you're not verified, and 0% if you hold gross payment status. Materials you billed to the contractor are excluded from the deduction, it only bites on the labour element. And materials means what the job genuinely cost you, HMRC's CIS340 guidance also keeps direct costs like consumable stores and plant hire you paid for outside the deduction, so don't let a contractor deduct on the whole invoice out of laziness.
Why most subbies are owed a refund
That flat 20% is a blunt instrument. It takes no notice of your personal allowance, the first £12,570 you earn tax free, and no notice of your expenses either. So all year you're being taxed on money that was never really profit. Come Self Assessment, your actual bill is worked out on profit after expenses and allowances, and the difference between what was deducted and what you truly owe comes back to you as a refund.
Take the default numbers in the calculator above. £45,000 gross with £5,000 of materials means CIS is deducted on £40,000 of labour, so £8,000 has already gone to HMRC at 20%. But with £12,000 of allowable expenses your taxable profit is only £33,000, and the tax and Class 4 NI actually due on that comes to roughly £5,300. That leaves around £2,700 sat with HMRC waiting to be claimed. Nice little bonus, except it was your money all along.
The 2025/26 numbers behind the estimate
| Item | Amount |
|---|---|
| Personal allowance | £12,570 (tapers above £100,000) |
| Basic rate 20% | £12,571 to £50,270 |
| Higher rate 40% | £50,271 to £125,140 |
| Additional rate 45% | Above £125,140 |
| Class 4 NI | 6% on £12,570 to £50,270, 2% above |
What about gross payment status?
With gross payment status, contractors pay you in full with nothing deducted at source, and you settle the whole lot through Self Assessment instead. It's brilliant for cash flow, but HMRC doesn't hand it out freely. You'll need to pass turnover, compliance and business tests, and keep your filing squeaky clean to hold onto it. If your CIS deductions routinely dwarf your real bill, it's worth a serious look.
How to claim your CIS refund, step by step
- Register for Self Assessment with HMRC if you haven't already. You'll get a Unique Taxpayer Reference (UTR), and nothing happens without it.
- Round up your CIS statements. Every contractor who deducts from you should give you a payment and deduction statement for each tax month they pay you. Chase any that are missing now, not in January when the contractor's phone mysteriously stops working.
- Total your income and expenses for the year to 5 April. Gross income from all contractors, then every legitimate cost: materials, van, fuel, tools, insurance, phone, the lot.
- File your return and enter the total CIS deducted in the CIS box. The online filing deadline is 31 January after the tax year ends, but you can file from 6 April, and you should.
- Get paid. Put your bank details on the return so HMRC can repay you directly instead of posting a cheque to wherever you lived two vans ago.
How long does a CIS refund take?
There's no statutory timescale, but the pattern is consistent: file a clean return in April or May with your bank details on it and the refund typically lands within a few weeks. File in the January rush and you're queueing behind everyone else who left it late. HMRC also runs security checks on some repayments, which adds time, and messy or missing paperwork is exactly what invites them. Tidy records, early filing, fast money. It really is that dull and that effective.
Three habits that make refunds bigger and faster
- Keep every CIS statement from every contractor. Refunds die without paperwork, and chasing a statement from a contractor who's gone quiet in March is nobody's idea of fun. Keep invoices, receipts, a mileage log and bank statements alongside them, HMRC expects self-employed records held for at least 5 years after the 31 January filing deadline.
- Claim everything legitimate. Mileage or van costs, tools, workwear laundering, phone, training, insurances, scheme fees. Every pound of missed expenses is a pound of refund left on the table.
- File early. The year ends 5 April, and April filers tend to get refunds back in weeks while January filers join the queue behind everyone else who left it late.
While you've got the calculator open, sense-check what you charge with my day rate calculator, a bigger refund is pointless if the rate underneath it is too low. And if you're more often on the tools than the spreadsheet, the kW to amps calculator and the rest of my free electrician tools are all one click away, no sign-up, no nonsense.
CIS refund FAQs
How much CIS refund will I get?
Depends entirely on your expenses and your personal allowance, the two things the flat 20% deduction ignores. Punch your numbers into the calculator above for a ballpark. In practice, plenty of subbies see £1,500 to £3,000 or more come back, especially in a year with heavy van, fuel or tool costs.
When can I claim my CIS refund?
Once the tax year ends on 5 April. You claim it through your Self Assessment return, and the refund is simply the gap between what contractors deducted and what you actually owed. The sooner you file after April, the sooner the money lands in your account.
How long does a CIS refund take?
File a clean return early with your bank details on it and it's typically a few weeks. There's no guaranteed timescale though, HMRC security checks can stretch it, and January filers wait longest because everyone else files then too. April filers get paid while January filers are still finding their receipts.
What records do I need to keep for a CIS refund?
The payment and deduction statement from every contractor for every tax month, plus invoices, expense receipts, a mileage log and bank statements. HMRC expects self-employed records kept for at least 5 years after the 31 January filing deadline, and a refund claim with no paperwork behind it is a security check waiting to happen.
Why am I on 30% CIS deductions?
Because you're not verified with HMRC. The 30% rate is the penalty lane for unverified subcontractors. Register for CIS, get verified by your contractor, and you drop to the standard 20%. That's a third less of your money sitting with HMRC all year, so sort it before your next payment, not after.
Do CIS deductions cover my whole tax bill?
Very often they more than cover it, which is exactly why refunds are so common. But don't bank on it blindly. A high earner with low expenses can burn through the deductions and still owe extra at the year end. Run the estimate above and you'll see which side of the line you're on.
What is gross payment status and should I get it?
It means contractors pay you gross, 0% deducted at source, and you pay everything through Self Assessment instead. Superb for cash flow, since you hold your own money all year rather than lending it to HMRC. The catch: strict turnover, compliance and business tests, and you have to stay compliant to keep it.
Do limited companies work differently under CIS?
Yes, completely different mechanics. A limited company offsets its CIS deductions against PAYE liabilities and Corporation Tax rather than claiming a Self Assessment refund like a sole trader. This calculator is built for sole trader subbies. If you're trading through a company, talk to your accountant about the offset.
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