A CIS refund can arise when deductions already withheld exceed the final Income Tax and National Insurance liability. Keep payment statements and claim the credit through the correct route. Neither a refund nor its amount is guaranteed simply because 20% or 30% was deducted.
Why a refund can happen
Contractors typically take 20% (if you are registered and can be verified) or 30% (if not) from labour payments. Your actual Self Assessment liability depends on total profit after allowable expenses, other income, allowances and reliefs. If CIS already covered more than that liability, the excess can come back as a repayment after the return is processed — or reduce what you still have to pay.
Illustrative only: £36,000 gross CIS labour in a year, £7,200 deducted at 20%, and after expenses your Self Assessment bill is £4,900. The £7,200 credits the bill; around £2,300 may be repayable once HMRC has matched the figures. Real outcomes depend on the whole return.
Sole traders and partners: Self Assessment is the main route
GOV.UK says sole traders and partners report total pay before CIS deductions as income, and report the deductions so HMRC can credit them. After the tax year ends, that usually happens on the Self Assessment return. For the form-level walkthrough, use CIS deductions on your Self Assessment return.
If you need money back during the tax year rather than waiting for the return, HMRC publishes form CIS40 for individuals. GOV.UK’s CIS40 guidance says to use the tax return instead once you are claiming after the year ends.
Limited companies are not on this Self Assessment path
Company subcontractors do not reclaim CIS through a personal Self Assessment return in the same way. GOV.UK directs companies to set CIS deductions against PAYE liabilities through payroll submissions (FPS/EPS). Do not try to clear company CIS on a personal return or by copying a sole-trader process. If you trade through a company, get payroll/CIS advice for that structure.
Evidence that actually matters
Keep every payment and deduction statement. Those figures are what you (or your accountant) total for the return. Bank “net” receipts alone are not enough — you need gross, materials, and deduction amounts. If statements are missing, chase the contractor first; HMRC’s CIS system also holds what contractors reported, but your own paperwork still matters.
Common mistakes
- Treating the 20% or 30% deduction as your final tax rate — see 20% vs 30% CIS deductions.
- Entering only net pay as turnover, which understates income and muddles the CIS credit.
- Ignoring expenses that reduce profit — and therefore can increase a refund. See CIS allowable expenses.
- Assuming gross payment status people get “refunds” of deductions that were never taken — they usually do not. See CIS gross payment status.
A CIS refund question is still a Self Assessment question. Being under CIS does not automatically put you into Making Tax Digital for Income Tax; that depends on qualifying income thresholds and HMRC’s timetable. Use the free MTD checker if your gross self-employment turnover is high enough that digital reporting may also apply.
TaxSimba’s Self Assessment service is accountant-led help for sole traders and partners who need CIS credited correctly on the return. We do not guarantee a refund amount or a payment date. Start Self Assessment with TaxSimba if you want that preparation handled.
Reconcile the credit before predicting a refund
Illustrative preparation example.
List CIS deductions by contractor and tax month, then compare the supported total with the draft return. Other income and liabilities still affect the final outcome. A repayment advert based only on the deduction percentage skips that wider calculation.
Check: Does the draft include all income and the evidenced CIS credit once?
| Check | Practical action |
|---|---|
| Are all deductions supported? | Reconcile the complete contractor statements to gross payments and bank receipts. |
| Is the annual tax calculation complete? | Include allowable expenses and other personal income before estimating a repayment. |
| Has HMRC processed and allocated the credit? | Check the account and any information requests before promising a payment date. |
Does a 30% deduction guarantee a larger refund?
No. Repayment depends on the full liability and credited amounts. A higher deduction affects cash flow but is not the final tax rate.
Do company subcontractors use this personal-return route?
No. Company CIS deductions have a different payroll and repayment process. Confirm the business structure before making a claim.
Download a checklist for this guide
- Collect every contractor's deduction statements.
- Reconcile gross payments and CIS credits.
- Gather supported business expense records.
- List other income and account balances.
- Record HMRC processing messages and repayment details securely.