A CIS tax refund is claimed by filing a Self Assessment return that reports your income, your allowable expenses, and the tax your contractors have already withheld. HMRC compares what was deducted from your payments against what you actually owe once the personal allowance, expenses, and National Insurance are factored in, then refunds the difference. Because contractors deduct 20% (or 30% if you’re unregistered) from every payment without accounting for any of those reliefs, most subcontractors end the year having paid too much.
Why You’re Almost Certainly Owed Money
Under the Construction Industry Scheme, contractors withhold tax from every payment to a subcontractor and send it to HMRC as an advance against your income tax and National Insurance for the year.1GOV.UK. Construction Industry Scheme (CIS) The deduction is a flat percentage of your labour: 20% for registered subcontractors, 30% if you haven’t registered. Nothing in that calculation reflects your personal allowance, your tools, your mileage, or your insurance.
Once you file, the picture changes. The personal allowance for the 2026/27 tax year is £12,570, so no income tax is due on the first £12,570 of taxable profit.2UK Parliament. Direct Taxes: Rates and Allowances for 2026/27 Every legitimate business expense reduces your profit further. The tax already withheld was calculated on turnover; the tax you actually owe is calculated on profit after the allowance. The gap is your refund.
Who Can Claim Through Self Assessment
The refund route through Self Assessment is for genuinely self-employed subcontractors. If HMRC decides you were really an employee, the contractor should have been operating PAYE rather than CIS, and the mechanism for recovering any deductions is different. The CIS tax taken from your payments still counts as tax paid either way.
How to File the Claim
There is no separate CIS refund form. You claim through your Self Assessment return using form SA100 together with the self-employment supplementary pages: SA103S for straightforward accounts, SA103F for more complex ones.3GOV.UK. Self Assessment Tax Return Forms The return reports your total income, your deductible expenses, and the CIS tax already deducted. HMRC cross-checks the deduction figure against what your contractors have declared, so it has to match.
That is what makes your payment and deduction statements the most important paperwork you own. Contractors must issue one within 14 days of the end of each tax month, showing the gross amount paid, any materials excluded, and the tax deducted.4GOV.UK. What You Must Do as a Construction Industry Scheme (CIS) Contractor Collect every one of them and add the deductions up before you file. If a statement is missing, ask the contractor to reissue it.
You’ll need your ten-digit Unique Taxpayer Reference and your National Insurance number to file. If you haven’t registered for Self Assessment before, register first through HMRC’s online services. Most subcontractors file through the Government Gateway.
Deadlines
For the 2025/26 tax year, which ended on 5 April 2026, the filing deadlines are 31 October 2026 for paper returns and 31 January 2027 for online returns.5GOV.UK. Self Assessment Tax Returns: Penalties You have four years from the end of the tax year to submit a return and claim overpaid tax. After that, the refund is lost no matter how much was overpaid, so unfiled years from earlier in that window are worth going back for.
Expenses That Grow the Refund
Every allowable expense reduces your taxable profit, which increases the refund. The legal test is that the expense must be incurred “wholly and exclusively” for the trade.6GOV.UK. Business Income Manual – BIM37007 – Wholly and Exclusively: Overview Anything with a mixed personal and business purpose usually fails unless the business share can be separated cleanly.
Tools, Equipment, and Protective Clothing
Hand tools, power tools, plant hire, and consumables all qualify. So does protective gear like hard hats, steel-toed boots, and high-visibility clothing. Repairs and replacement parts count too. Keep the receipts.
Travel and Mileage
Travel to temporary workplaces is deductible; an ordinary commute to a single permanent site isn’t. Most CIS work moves you between sites, so the bulk of your driving normally qualifies. From 6 April 2026, the approved mileage rate for cars and vans is 55p per mile for the first 10,000 business miles in the tax year and 25p per mile after that. Motorcycles are 24p per mile.7GOV.UK. Expenses and Benefits: Business Travel Mileage for Employees’ Own Vehicles The mileage rate covers fuel, insurance, servicing, and wear and tear, so you can’t also claim those costs separately. Parking, tolls, and public transport fares to temporary sites can be claimed on top.
Insurance, Phone, and Working From Home
Public liability premiums are deductible, as is professional indemnity cover where required. Accounting software, business phone bills, stationery, and postage all count. If you do invoicing or paperwork from home, HMRC’s simplified expenses give a flat monthly deduction: £10 for 25 to 50 hours, £18 for 51 to 100 hours, or £26 for 101 hours or more.8GOV.UK. Simplified Expenses if You’re Self-Employed: Working From Home Phone and internet aren’t included in the flat rate and are claimed separately based on the business proportion of the actual bill.
When the Money Arrives
After you submit the return, HMRC typically processes refunds within five days to eight weeks. Online filers are usually at the faster end. Payment goes to a nominated bank account or comes as a cheque to your registered address. If you owe HMRC anything from earlier years, that amount is taken off first and the balance is paid to you.9GOV.UK. What You Must Do as a Construction Industry Scheme (CIS) Subcontractor
If HMRC Reduces or Rejects the Refund
You have 30 days from the date of the decision letter to appeal. Use the form enclosed with the letter or write to the HMRC office named on it, explaining what you disagree with, what you think the correct figures are, and attaching any evidence.10GOV.UK. Disagree With a Tax Decision The original caseworker reconsiders first. If you still disagree, HMRC will offer an internal review by a different officer, and you can either accept that or take the case straight to the tax tribunal.
Refunds are most often reduced for three reasons: the CIS deductions you reported don’t match what your contractors declared, expenses were disallowed because they failed the “wholly and exclusively” test, or the return contained arithmetic errors. Checking your totals against every payment and deduction statement before filing prevents most of these.
Records to Keep
Self-employed records must be kept for at least five years from the 31 January following the tax year the return relates to. Records for the 2025/26 return, due 31 January 2027, need to be retained until at least 31 January 2032. Keep every payment and deduction statement, the invoices you issued, receipts for every expense claimed, bank statements, and a mileage log if you’re claiming vehicle costs. Digital copies are fine as long as they’re legible. If HMRC opens an enquiry, the burden is on you to prove your figures, and a missing receipt usually means the expense is disallowed.
Filing Late Costs Money Even When You’re Owed a Refund
The £100 fixed penalty applies from the day after the deadline whether you owe tax or are owed a refund. After three months, daily penalties of £10 start and can run up to £900. At six months and again at twelve months, HMRC adds 5% of the tax due or £300, whichever is higher.5GOV.UK. Self Assessment Tax Returns: Penalties A refund position is not a reason to delay; filing early in the tax year avoids the penalty risk entirely and gets your money back sooner.
Gross Payment Status as an Alternative
Subcontractors who qualify for gross payment status are paid in full with no deductions, which removes the wait for a refund altogether. Qualifying broadly requires a minimum level of construction turnover, a clean tax compliance record, and up-to-date Self Assessment filings; HMRC reviews the status annually and can withdraw it if you fall behind. You still file a Self Assessment return and pay whatever tax and National Insurance the calculation produces at year-end. What changes is the cash flow, not the total tax bill.