How to Claim Your CIS Refund Without an Accountant (2026 Guide)

Why CIS Subcontractors Almost Always Overpay

Under CIS, a contractor deducts 20% from your payments if you are registered (30% if you are not) and pays it straight to HMRC on your behalf. The deduction is taken from your labour (the materials portion of an invoice is excluded), but it is a flat 20% with no account taken of your Personal Allowance, your expenses, or your actual tax band.

For the 2025–26 tax year the Personal Allowance is £12,570: income you pay no tax on at all. CIS takes no notice of it: you are charged 20% from the very first pound. On top of that, your van, fuel, tools, insurance, protective clothing and other allowable costs all reduce your taxable profit, but they are not reflected in the 20% taken at source either.

The result is that the tax already collected through CIS is usually more than your final bill. When you file your Self Assessment return, HMRC compares the two and refunds the difference. A typical full-time subcontractor refund runs into four figures.

What You Need Before You Start

You will need your CIS deduction statements. Contractors must give you a statement for every payment period showing the gross amount paid, the cost of materials, and the amount deducted. Keep every one: the total of the "amount deducted" column is the figure that drives your refund.

You will also need a record of your income and your allowable business expenses for the tax year, your Unique Taxpayer Reference (UTR), and your National Insurance number. If you keep your income and expenses in software through the year, this part is already done.

Finally, you need to be registered for Self Assessment and, from April 2026 if your income is over the threshold, signed up for Making Tax Digital for Income Tax. You cannot reclaim CIS without filing a return.

How the Refund Is Actually Calculated

The calculation is simpler than it sounds. HMRC works out your total taxable profit (income minus allowable expenses), subtracts your Personal Allowance, applies Income Tax and Class 4 National Insurance to what is left, and arrives at your total liability for the year.

It then subtracts everything you have already paid, and CIS deductions count as tax already paid. If your CIS deductions are larger than your final liability, the balance is refunded to you. If they are smaller, you pay the difference.

You do not have to do this maths yourself. When your CIS deductions and your return are with HMRC, HMRC runs the calculation and tells you the figure. Your job is to make sure the numbers going in are complete and correct.

Do You Actually Need an Accountant?

Accountants typically charge a CIS subcontractor £250–£400 to prepare and file a return and claim the refund. For a straightforward subcontractor with CIS income and ordinary expenses, very little of that fee pays for genuine judgement. Most of it pays for data entry and submitting the return.

If your affairs are complex (multiple businesses, large capital purchases, property income, or anything you are unsure about), an accountant is money well spent. But if you are a sole-trade subcontractor with CIS statements and a list of expenses, you can record the figures and file the return yourself, and keep the £300.

The honest part: filing it yourself does not change the refund. The refund comes from HMRC either way. What you save is the fee for someone else pressing submit.

Claiming Your CIS Refund With FileThat

FileThat is built so a subcontractor can do this without tax knowledge. You record your income and expenses in the ledger through the year (free), and you enter each CIS deduction statement on the CIS Deductions screen: contractor name, employer reference, the period, gross paid, cost of materials, and the amount deducted.

When you file, FileThat submits your CIS deductions to HMRC through HMRC's official Construction Industry Scheme service and files your Self Assessment return. HMRC then runs the calculation and, if you have overpaid, processes your refund after the return is submitted.

There is no monthly subscription. The income and expenses ledger is free, and you pay a flat fee per filing, far less than a typical accountant's CIS return fee. You see the figures before anything is sent, so nothing goes to HMRC without you checking it first.

Common Mistakes That Delay a Refund

Missing CIS statements. If you leave a contractor's deductions off your return, you under-claim and leave your own money with HMRC. Chase any statements you are missing before you file.

Confusing materials with labour. CIS is only deducted on labour, so make sure each statement separates the cost of materials. Recording it correctly keeps your figures consistent with what the contractor reported.

Forgetting allowable expenses. Every legitimate expense you leave out raises your taxable profit and shrinks your refund. Tools, fuel, van costs, insurance, and protective gear all count.

Filing late. Refunds are processed after your return is accepted, so the sooner you file after the tax year ends on 5 April, the sooner the money comes back.