CIS subcontractor expenses you're probably not claiming (2026/27)

If you work under the Construction Industry Scheme, tax is taken off your pay before it reaches you. The contractor deducts 20% if you are registered, or 30% if you are not, and pays it straight to HMRC on your behalf.

What a lot of subcontractors do not realise is that the deduction is taken from your gross pay, before any of your expenses have been counted. HMRC has no way of knowing that you spent £200 on a new drill this month or drove 8,000 miles to get to site, so there is a good chance you have overpaid.

Once you file your Self Assessment and put your real costs in, most CIS subcontractors are owed money back. Below we set out, in plain English, what you can claim for 2026/27 and the few traps that catch people out.

Why most CIS subcontractors are owed a refund

Under CIS, the contractor treats your deduction as a payment towards your tax and National Insurance. If you are registered the deduction is 20% of your labour, and if you have never registered it rises to 30%.

The difficulty is one of timing. The 20% or 30% is worked out on what you were paid, before anyone has looked at your profit, and your profit is what is left after you have paid for tools, travel, insurance and everything else the job needs. Those costs are real, and they reduce the tax you owe.

When you file your return and enter your expenses, the tax due on your true profit is usually a good deal lower than the amount already deducted, and the difference comes back to you as a refund. It is worth knowing that the deducted tax is set against your whole bill, which includes both Income Tax and Class 4 National Insurance, so the amount that comes back is the balance after both have been covered, and it will not always be the full 20%.

A refund is the usual outcome, although it is not a certainty. If you have very few expenses, or other untaxed income alongside your CIS work, the deducted tax might only cover what you owe. For a rough idea before you do anything, our free CIS refund estimator will give you an approximate figure in a couple of minutes.

The expenses most subbies forget to claim

These are the costs HMRC accepts as allowable for a self-employed CIS subcontractor. It is worth going through the list carefully and being honest about what applies to you, because small amounts add up over a year.

• Tools and equipment, including drills, saws, hand tools and hire costs. Larger items of kit may be claimed in a different way, but they still count.
• Protective clothing and PPE, such as hi-vis, hard hats, gloves, goggles, ear defenders and knee pads.
• Work boots, provided they are safety boots. Ordinary shoes do not qualify.
• Vehicle costs, claimed either at 45p a mile for the first 10,000 business miles and 25p a mile after that, or as your actual running costs (fuel, insurance, repairs and tax). You need to choose one method and keep to it for that vehicle.
• Public transport to temporary sites, meaning train, bus or other fares to a site that is not your permanent base.
• Materials you paid for, meaning anything you bought yourself in order to complete a job.
• Your mobile phone, or at least the business-use share of the bill.
• Accountancy fees. Our fee for preparing your return is itself an allowable expense.
• Public liability insurance, along with any other genuine business cover.
• Use of your home for admin, meaning a reasonable amount for doing quotes, invoices and paperwork at home.
• Small tools and consumables such as blades, screws, drill bits and tape, which seem to disappear on every job.
• Laundry and cleaning of specialist workwear. This does not extend to your everyday clothes.
• Training that updates skills you already have, such as refresher courses and tickets that keep you current in your existing trade.
• Subsistence when working away, meaning reasonable food and drink for the times you are away from your normal base.

Mileage: usually the biggest one people undercount

Travel is the expense most subcontractors undercount. If you use your own van or car to reach different sites, you can claim 45p per mile for the first 10,000 business miles in the tax year and 25p a mile after that. You could instead claim the actual running costs together with a share of the vehicle's value, but for most subcontractors the flat mileage rate is easier to work with and is well worth recording.

Bear in mind that mileage is an allowable expense, so it reduces the profit you are taxed on and is not handed back pound for pound. A modest 8,000 miles a year at 45p comes to £3,600 of allowable expense, which at the basic rate is roughly £700 or more off your tax bill, with a Class 4 National Insurance saving on top, and all of that goes towards your refund. All you need is a record of your business journeys, and a phone log or a cheap notebook kept in the van is enough.

If you are not sure how the numbers compare with your CIS deductions, our tax calculators let you try out different figures.

The traps: what you cannot claim

A few costs feel as though they ought to count but do not, and claiming them is one of the quickest ways to attract a query from HMRC, so it is worth being clear about them.

• Ordinary everyday clothing, such as jeans, t-shirts or a normal jacket. Only proper PPE and specialist safety gear count.
• Commuting to a permanent workplace. Travel to a site you treat as your regular, fixed base is not allowable, although travel to a temporary site is.
• Fines of any kind, since parking tickets, speeding fines and penalties are never allowable.
• Meals on a normal working day at your usual site. Subsistence only applies when you are working away from your base.

Missing receipts aren't the end of the world

Nobody keeps every scrap of paper, and a missing receipt does not mean the cost was never incurred. Mileage is claimed at a set rate, so you do not need individual fuel receipts and a journey log is sufficient.

For other costs, bank and card statements are good evidence, and a reasonable, honest estimate for small consumables is better than claiming nothing at all. What HMRC expects is a fair return that you could defend if asked, and it does not have to be perfect.

From now on, it is worth photographing receipts on your phone as you go. It only takes five seconds, and it makes next year's refund quicker to prepare and larger.

How we sort it for you

We handle CIS subcontractors day in, day out. We gather your deduction statements together, pick up every allowable expense, file your Self Assessment and chase any refund that is due. Our fee is fixed and agreed before we start, so there are no unexpected bills, and when you ring you speak to Bobby directly; we do not use a call centre.

You can read more about how we work on our CIS accounting for contractors page, or get in touch and we will tell you roughly what you are owed.