CIS Tax Rebate Calculator — 2026-27
Construction Industry Scheme deductions of 20% or 30% are payments on account, not your final bill. Once your real expenses are counted, most subcontractors are owed money back.
Enter your gross CIS income, your business expenses, and what was actually deducted. The estimator works out income tax plus Class 4 National Insurance on your profit and compares it with the deductions.
Who this estimator is for
Self-employed subcontractors in the Construction Industry Scheme whose contractor deducts 20% (registered) or 30% (unregistered) from their pay before handing it over. It is not designed for contractors, limited companies offsetting CIS through payroll, or workers with gross payment status — those situations reconcile differently.
Expenses that legitimately shrink your tax bill
- Materials and consumables you paid for yourself (note: CIS deductions apply to the labour element — materials in your gross are reclaimed as expenses here).
- Van purchase or mileage, fuel, insurance, maintenance and parking for business journeys.
- Tools, equipment hire and personal protective equipment (PPE).
- Phone, professional insurance, accountancy and business bank charges — the business proportion.
- Training courses and CSCS-type cards required for the work.
From estimate to refund: the actual process
- Register for Self Assessment as self-employed if you haven't already (free on GOV.UK).
- Gather your CIS statements or payslips from every contractor — they show gross pay and deductions.
- File the return after 5 April: enter gross CIS income, the deductions suffered, and your expenses.
- HMRC calculates the real liability and repays the difference — typically within a few weeks of filing.
- File early in the tax year if you can: CIS refunds are among the fastest HMRC pays.
What this estimate can't tell you
- Class 2 NI and student loan deductions are excluded.
- If some income was outside CIS, include it in your real Self Assessment — this tool only models CIS income.
- The refund is finalised by HMRC when you file, not by this estimate.
The free HMRC route
Everything this calculator estimates can be claimed directly from HMRC at no cost — usually online in a few minutes or via a short form. Refund companies charge a percentage of money that is already yours. We never handle claims and are not affiliated with HMRC.