Been a contractor all my working life. As job "replacement", estimate on 35-40 weeks a year of billed work, that's what it is with all public holidays, leave,

Been a contractor all my working life. As job "replacement", estimate on 35-40 weeks a year of billed work, that's what it is with all public holidays, leave, professional development etc factored. Contractors often make more because they skip these and also work longer hours. If you need to pay medical and professional insurances it can easily be closer to 25-30 weeks a year billable after expenses, for estimating purposes. Short term contracts should be 20-40% more to allow for "gaps", in a hot market just another bonus, but you should stash this, if you get it. Also you still pay most insurances during the "gaps" so too many is bad news. Then if you think you are actually selling some service no one else is around to do, whatever mark-up you can defend. But go too high and you will suffer in a cold market unless you are remarkably good and everyone knows it. Or if you really know your domain and selling results (instead of direct effort/activity), then "double dip" as we say, do two contracts at same time and double the pay for maybe same or less work if you are lucky.