CIS Tax Rebate Calculator for Subcontractors

The CIS tax rebate calculator estimates the gap between the CIS tax your contractors deducted and the income tax due on your profit. Enter your gross income, allowable expenses and the CIS tax already taken. The result covers income tax only, so any Class 4 National Insurance still has to come off it.

For profit sitting in the basic-rate band, every pound of expense you can evidence is worth 26p: 20p off your income tax and 6p off Class 4 alongside it. That’s why the middle box does more work than the other two, and why a total you’ve guessed at costs real money.

This one’s for registered subcontractors working as sole traders or in a partnership. Three other things shift the answer: gross payment status, any PAYE work in the same tax year, and how much of your personal allowance it’s already used.

The figures also need to belong to one tax year: the personal allowance and the rate bands reset every 6 April, and a total straddling two won’t tell you anything.

What to enter in the CIS tax rebate calculator

Three figures go into the CIS tax rebate calculator, and the first one trips people up. Your gross pay is the full amount your contractors invoiced, counted before anything came off, rather than the sum that reached your bank.

Here’s what each box is asking for:

• Gross pay is everything your contractors paid you across the tax year, before CIS tax was deducted.
• Expenses is a single total of the business costs you can evidence, rather than a breakdown by category.
• Tax paid is the CIS tax your contractors deducted, which your monthly payment and deduction statements set out month by month.

For sole traders and partners, GOV.UK asks for income and deductions as two separate entries on the return: the full invoice totals in one field, the CIS tax withheld in another. The calculator mirrors that split, which is why you enter two numbers rather than one net figure.

The two won’t line up neatly, and that’s expected.

Your contractor applies the rate to the labour element alone, so several things come off the invoice before the percentage is applied: VAT, plant hire, consumable stores, fuel used for anything other than travelling, and materials you paid for directly. The guidance sets out what doesn’t count as your pay in full.

The practical effect: at the standard rate, the CIS tax on your statements is 20% of your gross pay at most, and less whenever your invoices carry VAT, materials or plant hire.

Worked for several contractors, or only part of the year? Add the statements together and enter the totals.

The calculator has no view of how many contractors were involved or which months you worked, only the yearly figures you give it.

The deduction covers National Insurance too

What your contractor withheld was never income tax on its own. GOV.UK calls these advance payments towards your tax and National Insurance bill, which means the sum on your statement was covering both.

Class 4 National Insurance is charged on the same profit your income tax is worked out on. For 2025/26 the self-employed National Insurance rates were 6% on profits between £12,570 and £50,270, and 2% above that.

On profit sitting in the basic-rate band, that puts 26p on every pound above the personal allowance rather than 20p.

Class 2 adds nothing where profits reach £6,845 or more, because HMRC treats those contributions as paid without you paying them.

National Insurance is the half the calculator leaves alone. It works out the income tax on your profit and stops there, so whatever Class 4 you owe still has to come off the figure it hands back.

What the CIS calculator leaves out

The CIS calculator is built from three figures, so anything outside those three sits outside the answer. Five things in particular:

• Class 4 National Insurance is not worked out, so the figure on screen is an income tax comparison rather than a refund.
• PAYE income, and the tax already deducted from it, don’t feed into the calculation.
• Payments on account towards the following year’s bill aren’t included, so a first return can leave you in a very different net position.
• Student loan repayments collected through Self Assessment don’t appear.
• Gross payment status means no deductions were taken at all, so there is nothing for the calculator to set your liability against.

Your tax code sits outside it as well. A code only applies to PAYE earnings, and CIS deductions run at a flat rate regardless of one, which is why the deduction and the bill land on different numbers.

Making Tax Digital doesn’t change any of that. Subcontractors inside MTD for Income Tax send updates through the year, and each update produces an estimate of the position so far rather than a repayment. The figure that settles is the one at the year-end declaration.

The making tax digital guide covers the thresholds and the dates.

A CIS tax rebate estimate, start to finish

A CIS tax rebate estimate is only as strong as the three figures behind it. Take a subcontractor invoicing labour only, with no materials in the mix, across the 2025/26 tax year.

Her contractors paid her £38,000 and deducted £7,600 at the standard 20%. Allowable costs came to £9,500, which leaves a taxable profit of £28,500.

Income tax runs on the £15,930 sitting above the personal allowance of £12,570. At 20%, that’s £3,186. Set that against the £7,600 already deducted and the calculator returns £4,414.

Her actual refund is lower than that. Class 4 National Insurance runs on the same £15,930 at 6%, which is £955.80, and Class 2 adds nothing because the profit clears the small profits threshold. Her real bill is £4,141.80 and her refund £3,458.20.

The £955.80 between those two figures is the Class 4 the calculator doesn’t subtract.

Change one input and the whole thing moves. Drop her expenses to £5,000 and the profit rises to £33,000. Her bill becomes £5,311.80 and her refund falls to £2,288.20. That £4,500 of lost costs took £1,170 off the refund, which is the 26p in the pound working in reverse.

HMRC recalculates all of this from the return itself. The figure above is what to expect, not what you are owed.

Why your CIS tax refund may differ

An estimate built on three inputs meets a return built on everything else you did that year. Four things pull the two apart:

• PAYE work in the same year uses part of your personal allowance, which leaves less of it to set against your CIS profit.
• Costs you can’t evidence come out of the expenses total, and HMRC can ask for proof before or after a repayment.
• A profit above £50,270 pushes part of the income into the higher rate, while the Class 4 rate on the excess drops to 2%.
• Payments on account can absorb a repayment instead of releasing it.

The CIS tax rebate calculator cannot see any of those, and none of them makes the estimate useless. It’s a figure to plan around rather than a figure to spend, and your return is where it gets settled.

Totalling your CIS allowable expenses

Your CIS allowable expenses go into the box as a single annual figure, so the work is in reaching that number rather than sorting it into categories.

HMRC’s test is whether a cost was incurred wholly and exclusively for the business. A cost failing that test does not belong in the total, however ordinary it looks on site.

Costs split between business and private use go in at the business share rather than the full amount, so the figure you need is a proportion rather than a receipt total.

Adding it all up covers a whole year of spending. Running costs arrive monthly and tools arrive in bursts, so a total built as you go rests on records, while one assembled the week before filing rests on memory.

Keep the evidence behind the figure, because the total is the part most likely to be queried. Which costs qualify, and the records that back them up, is set out in allowable expenses on your CIS tax return.

What to do after the CIS tax rebate calculator

An estimate is not a repayment, and the CIS tax rebate calculator produces the first rather than the second.

What it does is weigh the deductions on your statements against the income tax your profit attracts, working from three numbers and nothing else. Class 4 National Insurance is yours to take off afterwards.

Dig out the statements, work the yearly totals, decide which costs you can stand behind, and enter all three. What comes back is a planning number. The sum is settled on your return, and the figure that binds you arrives only after that.

The CIS tax refund guide covers the claim itself, from the three deduction rates through to the deadlines your return has to meet.

Key Takeaways

• The calculator compares CIS tax deducted against income tax alone, so take any Class 4 National Insurance off its figure before treating it as your refund.
• Gross pay means the full amount your contractors invoiced before deductions, not the sum that reached your bank.
• At the standard rate, CIS tax on your statements is 20% of gross pay at most, and less whenever your invoices carry VAT, materials or plant hire, because the rate applies only to the labour element.
• Class 4 National Insurance was charged at 6% on profits between £12,570 and £50,270 for 2025/26, on the same profit figure income tax uses.
• PAYE income, payments on account and student loan repayments sit outside the estimate, and gross payment status leaves nothing to compare.
• Quarterly updates under Making Tax Digital show an estimate of the position so far, not a repayment.