Fees plus bonus

[CoolCat]

Chance of this making a difference to IR35 status - Low
Chance of this putting you out of pocket because they don't pay up for whatever reason - High

This is nothing to do with you working practice or IR35 status. It's just a contractual agreement to make sure you don't piss off early. I'd not be taking this gig personally. There is only one way to get what you are due and too many to get screwed.

yes agree here

on the other hand, when I was the hiring manager I put bonus in the odd contract (on top of their normal day rate, not cut out of it), but it was a bonus simply on normal end of contract that would not pay out if the contractor left early, simply because it was critical that whoever we took on stayed until the end of the six months as the perm staff would be in other countries and not able to back fill easily. Worked out quite well the contractors stayed until the last day and did get a big bonus.

[LondonManc]

Also make sure the situation where the client terminates the contract early doesn't invalidate payment of the completion fee.

Massive point, well made. Binning you off two weeks before the completion date would be naughty.