Can someone explain the "24 month rule"?

[kryten22uk]

I keep hearing contractors referring to the "24 month rule". Can someone expand/explain this to me?

[kryten22uk]

So its purely and expenses thing? I thought that it might me something along the lines of, if you contract at the same client for 24mths or more then you fall foul of IR35 and will be classed as an employee. Hopefully this isnt the case.

[kryten22uk]

I've only been here 6mths and have signed for a further 6 mths. They may well offer an extension again, so I'll just have to decline.