Estimate your CIS refund before you file, know what HMRC actually owes you back.
For subbies on 20% or 30% who've had tax deducted at source and want a reasonable estimate of what they'll get back at self-assessment.
Sound familiar?
- “I've had thousands deducted over the year. I've no idea if I'm getting any back.”
- “My accountant says 'it depends' and I want a rough number now.”
- “I don't know if my van costs and tools actually get refunded.”
- “I'm on 30% because the main contractor never verified me. Am I getting all of it back?”
What this tool does
Takes your total CIS income, total deductions and expenses, and gives a rough estimate of the refund due after the tax bill is calculated. It is not a substitute for filing, but it tells you roughly what to expect.
Use the total before CIS, from your monthly CIS statements.
Add up the CIS tax taken off all year (the 20% or 30% on your payslips).
Rough guess is fine — include tools, travel, PPE, materials you paid for, phone, etc.
This is only an estimate based on the numbers you've entered and assumes basic-rate tax (20%). Your actual refund depends on your full tax return.
This tool doesn't include National Insurance, higher-rate tax, or more complex situations.
What this calculator assumes
- You're self-employed on CIS, not on PAYE
- All the income and CIS deductions you entered are for the full tax year
- You're on basic-rate tax (20%) and get the normal personal allowance (£12,570)
- It doesn't include National Insurance or any other income (PAYE, rental, etc.)
This is a ballpark figure — it's there to show whether you're likely due a refund and roughly how big, not to replace doing a proper tax return or speaking to an accountant.
What the law actually says
- •CIS deductions are payments on account of your tax and NIC bill, not a separate tax. Overpayments return at self-assessment as a refund.
- •Allowable expenses (van, fuel, tools, insurance, phone, business use of home) reduce your taxable profit and therefore increase the refund.
- •HMRC can withhold refunds if your returns or compliance record are open. Filing cleanly speeds it up.
- •Refund scams targeting construction workers are rife, do not pay a 'refund agent' 25% for something you can claim yourself or through a normal accountant.
What to do next
Get monthly SiteKiln updates?
One email a month. Rate changes, new tools, guide updates relevant to you. No spam, unsubscribe any time.