CIS Tax Rebate Calculator, 2026/27

How this is calculated

Self-employed subcontractors have CIS tax deducted from every payment before they receive it, at 20% or 30% of the labour element, regardless of their actual expenses or personal allowance. Because that deduction takes no account of allowable costs, most subcontractors have paid more than their real tax liability by the end of the year.

The calculator works out taxable profit by deducting allowable business expenses, such as tools, protective equipment, travel, subsistence, accountancy fees and a proportion of vehicle costs, from gross CIS income, then calculates the income tax due on that profit using the standard bands, and Class 4 National Insurance at the main and additional rates.

Comparing the CIS already deducted at source against this true liability shows the rebate due, or in some cases additional tax owed if too little was deducted or expenses were lower than expected.

What counts as an allowable expense

Tools and small equipment, protective clothing and safety wear, travel between sites, a reasonable proportion of vehicle running costs, public liability insurance, accountancy fees, and a proportion of phone and home office costs are all typically allowable for a CIS subcontractor.

Keeping receipts and a simple mileage or expenses log through the year makes the self-assessment return far more accurate and the rebate claim far more defensible if HMRC ever asks questions.

Claiming the rebate

The rebate is claimed through your self-assessment tax return, which must include your gross CIS income, expenses and the CIS tax already deducted, as shown on the monthly statements your contractor should have provided.

Filing early in the tax year, rather than waiting for the January deadline, gets any rebate paid out sooner, since HMRC generally cannot process a repayment until the return itself has been submitted and processed.

Why do CIS subcontractors usually get a refund?

Because CIS deducts tax at a flat 20% or 30% of labour income with no allowance for business expenses or the personal allowance, most subcontractors have more tax withheld during the year than their actual self-assessment liability turns out to be.

How long does a CIS rebate take?

Once your self-assessment return is filed and processed, HMRC typically issues a repayment within a few weeks, though this can take longer during busy periods or if the return is selected for further checks.

What if my expenses are higher than I estimated?

Higher genuine expenses reduce your taxable profit further, increasing the size of your rebate, so it is worth reviewing bank statements and receipts carefully rather than under-claiming allowable costs.

Do I need to register for self-assessment to claim?

Yes, you need to be registered as self-employed and file a self-assessment return each year to report your CIS income, expenses and deductions, and to trigger any repayment due.