Self-Assessment For CIS Subcontractors: Reclaiming Overpaid Deductions
Self-Assessment for CIS Subcontractors: Reclaiming Overpaid Deductions in the UK
Most people searching this topic are not looking for theory. They want to know three practical things: whether CIS deductions can be reclaimed, whether the claim goes on Self Assessment or somewhere else, and what to do when the contractor, HMRC, or the paperwork does not line up. HMRC’s current guidance still treats CIS deductions as advance payments towards the subcontractor’s tax and National Insurance, not as a separate tax in their own right. For the 2025/26 tax year, the SA100 return covers income from 6 April 2025 to 5 April 2026, and the standard deadline for submitting that return is 31 January 2027.
How CIS deductions work in practice
Under CIS, a contractor normally deducts money from a subcontractor’s payment and sends it to HMRC. If you are a registered subcontractor but do not have gross payment status, the usual deduction rate is 20%. HMRC applies 30% where you are not registered, cannot be verified, or give the wrong business name. Contractors should also give you monthly statements showing what they paid you and what they deducted, because those statements are the core evidence for your tax return.
That point matters because the deduction is only meant to apply to the taxable element of the payment. Contractors should not deduct CIS from amounts on your invoice for VAT, plant hire, consumable stores, manufacturing or prefabricating materials, or materials you paid for directly. If a contractor deducts too much because they included non-deductible items, used the wrong rate, or failed to verify you correctly, the over-deduction is still reclaimed through the tax system rather than dealt with as a private refund from the contractor.
The Self Assessment route depends on who you are
For sole traders and partners, HMRC is clear: at the end of the tax year you send in your Self Assessment tax return as usual. On that return you enter the full amounts on your invoices as income and then include the CIS deductions in the CIS deductions field. HMRC then calculates your Income Tax and National Insurance bill and offsets the CIS deductions against it. If you still owe tax, you pay the balance by 31 January after the end of the tax year; if you are due a repayment, HMRC sends it back.
The key trap is that the return must show gross income, not the net amount you actually received after deduction. HMRC’s 2026 self-employment notes say subcontractors must include the full amount before CIS deductions when recording turnover, and then separately add up the deductions taken by contractors from the relevant tax year’s statements. The notes also say you should not send those statements with the return.
For the 2025/26 return, HMRC’s supplementary pages follow the same pattern but the box number depends on which self-employment pages you use. In the short pages, CIS deductions go in box 38; in the full pages, they go in box 81. If you have already claimed a CIS repayment in-year, HMRC still expects the deductions to appear on the tax return as well, with any refund already received disclosed in the “tax refunded or set off” box.
Limited companies work differently. HMRC says company subcontractors do not reclaim CIS deductions through the Corporation Tax return. Instead, the company claims the deductions through its monthly payroll filing process using FPS and EPS submissions, and any deductions not used up against PAYE and National Insurance can be carried forward within the tax year. If a company tries to claim CIS deductions through Corporation Tax instead, HMRC warns that a penalty may follow.
When a repayment is actually due
A CIS repayment is due when the deductions already collected during the year are greater than your final tax and National Insurance liability. That can happen for straightforward reasons: the business had a quiet year, allowable expenses were higher than expected, there were gaps between contracts, or too much was withheld because the contractor used 30% instead of 20%. The fact that you have had deductions taken does not mean you have overpaid overall, but it often does mean you need to complete the return properly to find out.
Gross payment status changes the picture entirely. HMRC says contractors then pay you in full, without CIS deductions, and you pay your tax and National Insurance at the end of the tax year. To qualify, you must meet HMRC’s tests on tax compliance, UK construction activity, and banking arrangements, and your turnover must meet the relevant thresholds. For many subcontractors, gross payment status is not the quickest fix to an over-deduction already suffered, but it is the clearest way to reduce deductions going forward if the business is consistently compliant.
The 2026 timing points that matter
If you are filing for 2025/26, the Self Assessment year runs to 5 April 2026. HMRC’s notes say paper returns must reach HMRC by 31 October 2026, and the tax notes for 2025/26 state that if the paper return is received by the deadline, HMRC will calculate the tax and tell you before 31 January 2027. The official Making Tax Digital timeline also shows 31 January 2027 as the deadline to submit the 2025/26 Self Assessment return the usual way.
This timing is more important than it looks. If you submit too early, before all contractor statements are received or reconciled, you can underclaim and then have to amend later. HMRC’s CIS pages specifically say that if you do not have all the CIS statements you need, you should ask the contractor for duplicates; if the contractor has stopped trading, you should write to HMRC with the contractor details and the dates of payment. That is the right route when the paperwork is incomplete, not guessing the figure and hoping it matches later.
For in-year claims, HMRC also distinguishes between a current-year repayment claim and the end-of-year Self Assessment route. Form CIS40 is for an individual claiming repayment during the current tax year; if you are claiming after the tax year ends, HMRC says to use your tax return instead. That distinction matters because many subcontractors search for a refund form when they actually need to complete Self Assessment.
Common mistakes that delay or reduce repayments
The most common error is reporting the wrong income figure. HMRC’s notes are explicit that the turnover figure should be the gross amount before CIS deductions. If you enter only the amount that landed in your bank account, the return will understate turnover and can distort the repayment calculation.
The second error is relying on memory rather than statements. HMRC expects subcontractors to total the deductions shown on the contractors’ monthly statements. If statements are missing, the figures should be chased and reconciled rather than estimated casually. HMRC may ask for evidence, and if you do not provide it by the deadline they set, it can correct the claim and stop further claims for that tax year.
A third issue is mixing up the reclaim route. Sole traders and partners claim through Self Assessment; current-year claims use CIS40; company subcontractors use payroll submissions, not the Corporation Tax return. Because these routes are different, a good claim can still be delayed if it is sent through the wrong channel.
Another subtle problem is failing to show the full amount before deductions in the accounts or self-employment pages. HMRC’s 2026 notes say subcontractors should include the full amount before CIS deductions in turnover, and then separately include the deductions in the CIS box. That sequencing is what makes the repayment calculation work correctly.
A realistic example
Suppose a sole trader subcontractor invoices £36,000 before CIS deductions during 2025/26 and receives monthly deduction statements totalling £7,200 at the standard 20% rate. The return should show the £36,000 as turnover, not the net amount banked. After business expenses and the rest of the tax computation are completed, HMRC offsets the £7,200 against the final bill. If the final tax and National Insurance liability is lower than £7,200, the difference becomes the repayment. If it is higher, the subcontractor pays the balance by the normal Self Assessment deadline. The repayment result depends on the final tax calculation, not just the CIS total by itself.
That example also shows why CIS refunds are often overstated in casual conversations. A subcontractor can have a large CIS deduction total and still owe tax once profits, other income, Class 4 NIC, and any other liabilities are calculated. CIS is an advance payment mechanism, not a guaranteed refund pool.
Practical checks before you file
Before submitting the return, make sure the legal or trading name given to each contractor matches the CIS registration details, because HMRC says the wrong name can trigger the 30% deduction rate. Check that each contractor statement has been included, and that the total deduction figure agrees with the Self Assessment pages. If you have gross payment status, check that you have not accidentally entered deductions that should not exist at all. And if you have already had an in-year refund, make sure it is reflected correctly on the return rather than being counted twice.
For many subcontractors, the best habit is to reconcile CIS every month instead of once a year. That does not change the tax law, but it reduces the chance of missing statements, duplicating deductions, or finding out in January that the records are incomplete. HMRC’s own guidance assumes you are keeping the monthly statements and using them to work out whether you owe tax or are due a repayment.
Summary of key insights
CIS deductions are advance payments, so over-deducted amounts can be reclaimed, but only through the correct route. For sole traders and partners, that route is Self Assessment; for current-year claims, HMRC uses CIS40; and for limited companies, CIS deductions are reclaimed through payroll reporting rather than Corporation Tax. The return should always show gross income before CIS deductions, with the deduction total entered separately from contractor statements. For 2025/26, the filing timetable is 31 October 2026 for paper returns and 31 January 2027 for online submission.
The practical lesson is simple: match the contractor statements, use the right form or return, and do not let net bank receipts replace the gross figures in your records. That is usually the difference between a clean repayment and a delayed one.
FAQs
Q1: Can someone still reclaim CIS deductions if a contractor never issued monthly CIS statements?
A1: Well, it’s worth noting that HMRC does not remove a subcontractor’s entitlement to claim simply because the paperwork is missing. The difficulty is proving the deductions actually happened. In practice, the first step is usually to ask the contractor for duplicate statements covering each tax month.
If the contractor has ceased trading or refuses to cooperate, HMRC may still accept alternative evidence such as bank entries, invoices, site payment schedules, or emails confirming deductions. I’ve seen this happen where a subcontractor in Newcastle worked for a small building firm that folded mid-year. The monthly statements disappeared with the business, but HMRC eventually matched the deductions against the contractor’s CIS submissions.
The key point is this: the subcontractor should not guess figures casually. CIS claims are increasingly checked against contractor filings before repayments are released.
Q2: Can someone lose a CIS refund because the contractor used the wrong UTR number?
A2: Yes, and this catches out more people than you might expect. If the contractor files CIS returns using incorrect subcontractor details, HMRC’s systems may not match the deductions to the right taxpayer record.
In my experience with clients, this often surfaces months later when a repayment is delayed “pending verification”. A common scenario is one incorrect digit in the UTR or a mismatch between trading name and legal name.
Usually the contractor must amend their CIS returns before HMRC releases the repayment. It’s one reason subcontractors should check their CIS statements throughout the year instead of waiting until January.
Q3: Can a CIS subcontractor claim a refund if they also have PAYE employment?
A3: Absolutely. A surprising number of construction workers move between subcontracting and PAYE employment during the same tax year. HMRC treats these as separate income sources within the same Self Assessment return.
A realistic example would be someone working under CIS for eight months and then taking a salaried site manager role for the remainder of the year. CIS deductions may already cover much of the eventual tax liability, especially if PAYE also deducted tax correctly.
The complication is that PAYE income can reduce or eliminate the expected refund. Quite a few subcontractors wrongly assume CIS deductions automatically generate repayments, without considering salary income, bonuses, benefits, or company car tax.
Q4: Can someone reclaim CIS deductions if they worked abroad for part of the year?
A4: Potentially, yes. The real issue is UK tax residence and whether the construction income remains taxable in the UK.
I’ve dealt with subcontractors who spent several months working in the Middle East or Ireland while still undertaking UK CIS work before departure. In those situations, HMRC still expects the UK CIS income to be reported correctly.
Where double taxation agreements apply, specialist advice becomes important because foreign tax treatment can affect the final liability. Many people assume “working abroad” automatically removes UK obligations, but CIS deductions already suffered in the UK still need proper reconciliation through Self Assessment.
Q5: Can a subcontractor claim travel costs between different building sites?
A5: Usually yes, provided the travel qualifies as allowable business travel rather than ordinary commuting. This distinction matters far more than most subcontractors realise.
Travel from home to a genuinely temporary site is commonly allowable. However, if someone works at the same site continuously for a long period, HMRC may start viewing it as a permanent workplace.
I’ve seen disputes arise where subcontractors claimed mileage to one site for nearly two years. At that point, HMRC questioned whether the site was really temporary anymore. Good mileage records and job allocation evidence make a major difference during enquiries.
Q6: What happens if a subcontractor forgets to include one contractor on their tax return?
A6: It’s a common mix-up, particularly for subcontractors working with multiple firms over a busy tax year. The return can usually be amended after submission if the omission is discovered in time.
The risk is not just underreporting income. Sometimes the missing contractor also means missing CIS deductions, which changes the repayment figure entirely.
One electrician I advised had included the income from a contractor but forgot the CIS deducted. The result was an unexpected tax bill instead of a refund. Once corrected, the position reversed completely.
Q7: Can HMRC hold a CIS refund for compliance checks even when the figures are correct?
A7: Yes, and this has become increasingly common. HMRC frequently cross-checks CIS deductions against contractor submissions before issuing repayments.
First-time filers, unusually large repayments, mismatched deduction totals, or frequent amendments can all trigger additional checks. Sometimes the refund simply sits in pending status while HMRC reviews the contractor data.
That does not automatically mean something is wrong. However, if months pass without progress, it is often sensible to contact HMRC or ask an accountant to review whether a mismatch exists behind the scenes.
Disclaimer
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