CIS tax rebate guide: claim it yourself, free

Construction contractors deduct 20% (registered) or 30% (unregistered) from subcontractor pay and hold it for HMRC. That deduction is not your tax bill — it's a deposit calculated on your gross income, ignoring every expense you have. File a return that counts the expenses properly and the difference comes back. Average real-world CIS refunds sit comfortably in the £2,000–£3,000 range per year, which is why an entire industry exists to charge you a cut of them. Filing is free; this is how it all works.

Why the scheme produces refunds by design

	With CIS deduction	Your real tax bill
Basis	Gross income, flat 20%	Profit after expenses, through bands
Allowance	None applied	£12,570 Personal Allowance applied
Expenses	Ignored	Fully counted

Worked example, 2025-26, a subcontractor with £30,000 gross and £7,000 of genuine costs:

• CIS deducted: £30,000 × 20% = £6,000
• Profit: £30,000 − £7,000 = £23,000
• Income tax: (£23,000 − £12,570) × 20% = £2,086
• Class 4 National Insurance: (£23,000 − £12,570) × 6% = £625.80
• Real liability: £2,711.80 → refund: about £3,288

Generalise it and the pattern holds: at £7,000 of expenses the system over-collects by roughly 20% of expenses plus the allowance effect. Zero expenses and £30k gross? The refund shrinks to the allowance effect (about £1,800–£2,900 depending on NI). Our CIS calculator runs your precise numbers, National Insurance included.

Expenses that count — and the traps inside them

The test for every cost is "wholly and exclusively for the business":

• Materials you paid for yourself. Note the CIS mechanics properly: contractors deduct only on the labour element if materials were identified in the invoice — but many invoices blur it, and the materials comeback happens here on your return either way.
• Van, fuel and travel between sites. Choose mileage (55p/25p from 2026/27; 45p/25p before) or actual costs — not both. Daily travel to one long-term site can count as commuting if that site becomes your regular workplace.
• Tools, equipment hire, PPE. Small items straight through as expenses; big kit via capital allowances — 100% relief in year one under the Annual Investment Allowance for almost anything a subcontractor buys.
• Phone, insurance, accountancy, business bank charges — the business proportion only.
• Training and cards (CSCS renewals, safety courses) required for the work.

Never claimable: ordinary clothing, lunch on normal working days, fines, the weekend van trip to B&Q that was really for the house.

The free claim, step by step

1. Register for Self Assessment as self-employed (sole trader) if you haven't — free on GOV.UK, takes about ten minutes and a few days for codes to arrive.
2. Collect evidence: CIS payment and deduction statements from every contractor (they must supply them monthly), plus receipts for expenses.
3. File after 5 April: income section = gross CIS, deductions suffered box = the 20/30% withheld, expenses section = your costs.
4. HMRC reconciles and repays the over-deduction — typically within a few weeks; CIS refunds are among the fastest HMRC processes because the withholding is already sitting with them.
5. File early. Nothing requires waiting until January; filing in April/May means refund in spring.

Unregistered at 30%? Fix that first

Registration isn't just admin: it's the difference between 30% and 20% deductions on every pound — on £30,000 that's £3,000 less of your cash held hostage all year. Register for CIS as a subcontractor free on GOV.UK with your UTR and NI number; the rate drops from your next payment.

Gross payment status: the end state to aim for

Establish a clean filing and payment record (HMRC checks late returns, late payments, turnover and the "business test") and you can apply for gross payment status — contractors pay you in full, no deductions, and you simply pay tax through Self Assessment like any other sole trader. Your cash flow transforms overnight, and you settle your tax on your own schedule. It's free to apply and reviewable annually.

When an accountant is worth paying (and when it isn't)

A good accountant earns their fee when you have: incomplete records, a limited company, employees of your own, property income, or an HMRC enquiry open. For a straight "one trade, statements in hand, receipts in a folder" CIS year, the free HMRC route plus your own discipline does the identical job — HMRC's Self Assessment helpline walks people through the boxes every day.