Work out in 30 seconds what you owe or what you are owed, on your own figures, then download the answer as a PDF and keep it. No account and no payment.
You are not taxed on everything you are paid. You are taxed on profit, which is what is left after you take off the cost of working: tools, travel, materials, work clothes. The better you keep track of what you spend, the smaller the profit and the smaller the tax.
The first slice of that profit is not taxed at all. Above it, income tax starts, and National Insurance is charged separately on top. The calculator applies both and shows you the total.
Under CIS your contractor takes 20% off your pay and sends it straight to HMRC, the tax office. It comes off the whole amount, not off your profit, and it takes no account of the part of your income that is not taxed at all.
That is why, by the end of the year, a lot of people have already paid more than they owe. The difference can be claimed back. The calculator tells you whether that is you, and by how much.
Two things decide how much comes back: the expenses you can prove, and the CIS statements that show what was taken. Without them the answer stays an estimate.
The official rates for the tax year 2026/27, read off GOV.UK: the personal allowance, the tax thresholds and Class 4 National Insurance. They change once a year, and the calculator carries the ones in force now.
It applies them exactly as written, including the way the personal allowance tapers away above £100,000, which is easy to miss doing it by hand and moves the answer by thousands.
For anyone under CIS watching 20% come off every payment without knowing whether they end the year up or down. For anyone who has just started working for themselves and has no idea what to expect in January. And for anyone with a limited company who wants a rough figure before the conversation with their accountant.
If that is you, thirty seconds here gives you an order of magnitude you would otherwise not see until filing day.
It is an estimate, not a tax return. It starts from the figures you type in and assumes this is your only income; if you also have a job with tax taken at source, the answer changes. It sends nothing to HMRC.
How close it gets depends almost entirely on one thing: how well you know your own figures. That is usually where it breaks, not in the arithmetic. Lost receipts, CIS statements left in the van, mileage nobody wrote down. Every cost you cannot prove stays in your profit and gets taxed.
That is what Farul does all year: it keeps your receipts, your CIS statements and your mileage in one place, so that when you type figures in here they are your real ones and not what you remember. And if you want to talk to a person, we can put you in touch with an accountant.
Seven days free, no card. See what your tax year looks like when it no longer depends on memory.
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