Port Accounting Services Limited Useful Tools

CIS Rebate Calculator — estimate your refund or balance

Rates: 2026/27

If you're a subcontractor in the Construction Industry Scheme, the 20% (or 30%) your contractor withheld wasn't your final tax bill — it was tax paid on account. Once your expenses and allowances are taken into account, that may leave a refund due, or a balance still to pay.

Enter what you earned, what was withheld and what you spent running the job, and this tool estimates your 2026/27 position — whether a refund may be due, or more tax is payable. It is an estimate based on the figures you provide and the assumptions listed below, not a calculation of your actual liability.

Your figures

The full amount on your CIS payment statements, before tax was deducted.

The total 20% (or 30%) withheld by contractors across the year.

Any non-CIS work, cash jobs or day rates.

Tools, materials, van costs, PPE, mobile (business portion) and accountancy fees. Don't include mileage here.

Business miles in your own vehicle. We apply HMRC's 55.00000000000001p/25p approved rates.

Wages or pension income taxed under PAYE this year.

Your repayment plan is shown on your loan statement or payslip.

Gross personal pension contributions paid in the year. These extend your basic-rate band.

Enter your figures above

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Tax year 2026/27 · figures as at 26 August 2026

How this is calculated
  1. Gross CIS incomeTotal on your CIS payment statements before deductions£0
  2. Other self-employed income£0
  3. Allowable business expensesDeducted from income−£0
  4. Mileage allowance55.00000000000001p per mile for the first 10,000 miles, then 25p−£0
  5. Self-employed profitIncome less expenses less mileage£0
  6. Other taxable income£0
  7. Total income£0
  8. Personal allowance£12,570, reduced by £1 for every £2 of income above £100,000−£12,570
  9. Taxable income£0
  10. Income tax20% to £50,270, 40% to £125,140, 45% above£0
  11. Class 4 National Insurance6% on profit between £12,570 and £50,270, 2% above£0
  12. Student loan repaymentNo plan selected£0
  13. Total tax due£0
  14. CIS tax already deducted−£0
  15. Estimated refund£0

Assumptions used

  • England, Wales and Northern Ireland income tax rates for 2026/27 (Scottish rates differ).
  • Mileage claimed at HMRC approved rates for your own vehicle; not combined with actual vehicle running costs.
  • Gross personal pension contributions extend your basic-rate band.
  • Class 2 NI, payments on account, and prior-year adjustments are not included.
  • Assumes all CIS deductions shown on your statements have been reported by contractors.

Want your estimate checked and the return filed?

Any refund is claimed through a Self Assessment return. We file these for CIS subcontractors regularly, and can check your figures and records before anything goes to HMRC. HMRC sets its own processing times, and the amount they repay may differ from this estimate.

Book a 15-minute chat

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Estimate only. This is not a calculation of the amount HMRC will repay, and no refund is due until HMRC has processed your Self Assessment return. If you have rental income, capital gains, or income over £100,000, the position is more involved — speak to us before relying on the figure.