Roughly what you are owed back for a tax year, once your costs and your personal allowance are set against what was deducted at source.
Everything you invoiced on construction work, excluding VAT.
If it changed part-way through the year, pick the one you were on longest.
Add up the deduction column on your payment and deduction statements. Leave it at zero and we will estimate it from your turnover.
Only materials you directly incurred. Materials the contractor bought and recharged do not reduce the deduction.
Van, fuel, tools, protective equipment, phone, insurance, subscriptions, accountancy. The full list is on the what-you-can-claim page.
Employment or rental income. It uses your personal allowance first, which makes the refund smaller.
Illustrative figures on 2026/27 rates and simplified assumptions. This is information, not advice, and it is no substitute for a proper calculation on your practice's real numbers. Ask us for the accurate version — it's free.
What this is doing
There is no separate CIS refund claim. The deductions your contractors took are advance payments towards your income tax and Class 4 National Insurance. You file a Self Assessment return, those payments are set against what you actually owe, and HMRC repays the excess.
That is why the size of a refund is decided by three things the deduction knows nothing about: your personal allowance, your costs, and whether you had other income using the allowance up first.
It uses 2026/27 rates for England, Wales and Northern Ireland — personal allowance £12,570, basic rate 20% on the first £37,700, higher rate 40%, and Class 4 National Insurance at 6% between £12,570 and £50,270. It does not account for student loan repayments, payments on account, capital allowances on a van or plant, losses brought forward, or Scottish income tax rates. Every one of those moves the number and none of them can be worked out from six boxes.
So treat the figure as an indication of whether there is something worth claiming, not as the number that will land in your bank.
A large repayment means you lent HMRC money interest-free for up to twenty months. For a labour-only subcontractor, gross payment status removes the deduction entirely and you keep the cash through the year.
It is an indication rather than a calculation of your return. It applies 2026/27 rates for England, Wales and Northern Ireland to six figures. It does not know about student loan repayments, payments on account already made, capital allowances on a van or tools, losses brought forward, or Scottish rates — and each of those changes the answer. Use it to see whether there is something worth claiming, then get the real number worked out.
Yes — leave the deducted figure at zero and it estimates from your turnover and the rate you were on. That is good enough to tell you whether it is worth chasing. It is not good enough to file, because the statements are the only document showing what was actually taken and on what basis, and HMRC will compare your figures to what your contractors reported.
Because the personal allowance is a single fixed amount across all your income, not one per source. Wages from a job use it up first, which leaves less of it to shelter your self-employed profit, so more of that profit is taxed and less of the CIS deducted comes back.
It can be. It usually means your costs were low relative to turnover, or a good part of your income was outside the scheme and had nothing deducted from it. It can also mean the figures typed in are not the ones on your statements. Either way it is worth checking properly before the January deadline rather than after it.
These tools use sensible simplifications. A free CIS review gets you the accurate version — and usually two or three things worth fixing before your year end.