About us: IR35 Calculator
Most contractors discover IR35 the hard way. A friend gets investigated. An accountant flags something on a self-assessment. A client suddenly issues an inside determination with no warning. We built the IR35 Calculator because that does not have to be the starting point.
Why we built this
The existing resources around IR35 fell into two camps. Either they were buried in HMRC guidance that reads like it was written for tax lawyers, or they were produced by firms that want to sell you something at the end.
We wanted a third option. A free tool with no agenda behind it. Something a contractor could use on a Sunday afternoon before signing a contract on Monday morning.
That is what this site is.
What the calculator actually does
You put in your day rate. You tell the tool whether your contract is inside or outside IR35. It shows you the take-home difference, income tax, National Insurance, effective rate, and monthly and annual figures.
No signup. No email address required. No upsell at the end. The numbers are based on current UK tax rates and standard PAYE assumptions, and we update the tool when those rates change.
Who this is for
Contractors running the numbers before they sign
You want to know what you actually take home before you commit to a rate. That is the most common reason people land here, and the calculator answers it in about thirty seconds.
Contractors comparing two offers
One contract is outside IR35 at £500 a day. Another is inside IR35 at £600. Which one puts more in your pocket? The calculator tells you without requiring a spreadsheet.
Anyone who just wants to understand IR35 better
The site covers more than the calculator. If you want to understand what inside and outside IR35 actually mean, how status gets decided, and what the three key tests are, the content on this site covers all of it in plain English.
What we are not
We are not accountants. We are not a law firm. We do not give regulated financial or tax advice.
The calculator is a starting point — a way to understand the numbers before you speak to a professional. For anything complex or borderline, an IR35 specialist will always give you something we cannot: advice that is tailored to your actual contract and working practices.
We are straight about that because we think it matters. A tool that oversells what it can do is more dangerous than no tool at all.
How we keep it accurate
IR35 has changed a lot since it was introduced in 2000. The 2017 public sector reforms shifted responsibility for status decisions to end clients in the public sector. The 2021 private sector changes extended that to medium and large businesses across the board.
We follow those changes closely. When HMRC updates its guidance or tax thresholds shift at the start of a new tax year, we update the calculator to reflect it. If you ever spot a figure that looks off, there is a contact page, and we take those messages seriously.
Our IR35 content is reviewed by Lewis Bennett, an employment tax specialist with more than a decade of experience in PAYE compliance and contractor taxation.
One thing worth knowing
The calculator tells you the financial difference between inside and outside IR35. It does not tell you which one applies to your contract. That is a legal question based on your actual working arrangement — things like whether you can send a substitute, who controls how the work gets done, and whether there are ongoing obligations on both sides.
If you want to understand what those tests mean and how they are applied, you will find a full breakdown elsewhere on the site. And if you want to know how we handle the data you enter, our privacy policy explains it without the legal fog.
The short version
Free tool. No catches. Built for UK contractors. Updated when the rules change. Honest about what it can and cannot do.
That is the whole thing.
See what you would actually take home.
Enter your day rate once and compare inside and outside IR35 side by side. Free, no signup.