Why do CIS subcontractors usually get a refund?

CIS deducts 20% (or 30%) from your labour throughout the year, often more than your actual tax bill once your tax-free Personal Allowance and business expenses are taken into account. The overpayment is refunded after you file your Self Assessment.

How is my CIS refund worked out?

Your profit (income minus expenses) is taxed via Income Tax and Class 4 National Insurance. The CIS already deducted from your pay is set against that bill. If the CIS deducted is more than the tax due, the difference is your refund.

When can I claim my CIS refund?

After the tax year ends on 5 April, once you have your CIS deduction statements. You claim it through your Self Assessment tax return; HMRC then refunds any overpayment.

Is this calculator exact?

No — it is a guide using standard tax bands and a simplified National Insurance calculation. Your actual figure depends on your full circumstances and current HMRC rates. Always check with an accountant or HMRC before relying on a number.

Free CIS tool

CIS Tax Refund Calculator

Most CIS subcontractors are owed money back. Pop in your year's figures for a quick estimate of your refund.

Total income (labour, before CIS)

CIS deducted this year

Business expenses (tools, fuel, materials…)

Personal allowance (tax-free)

Taxable profit

£0

Tax + NI due

£0

Estimated refund
£0

Estimate only — uses standard bands (20%/40%) and simplified Class 4 NI. Not tax advice; check with HMRC or an accountant.

Why subcontractors get CIS refunds

Under CIS, contractors take 20% (or 30% if you're not registered) off your labour all year and pass it to HMRC. But that's usually more than you actually owe, because:

Your first £12,570 of profit is tax-free (the Personal Allowance).
Your business expenses — tools, fuel, materials, insurance, phone — reduce your taxable profit.

When you file your Self Assessment after 5 April, the CIS already deducted is set against your real tax bill, and HMRC refunds the difference.

How this estimate works

We take your income, subtract expenses to get your profit, then work out Income Tax (20% above your allowance, 40% above the higher-rate threshold) plus a simplified Class 4 National Insurance figure. Your CIS deducted minus that bill is your estimated refund (or the extra you'd owe, if negative).

CIS refund FAQs

Why do I usually get a refund? +

CIS deducts a flat 20% from labour, which is often more than your real bill once your tax-free allowance and expenses are counted.

How is it worked out? +

Profit (income − expenses) is taxed via Income Tax + Class 4 NI; the CIS already deducted is offset against it, and any overpayment is refunded.

When can I claim? +

After 5 April, through your Self Assessment, once you have your CIS deduction statements.

Is this exact? +

No — it's a guide using standard bands and simplified NI. Check with HMRC or an accountant before relying on it.

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