Maybe it's not a real contractor. I had one job where I was a "contractor", I had set hours, got paid hourly, received a w2. It seemed like just an excuse to be cheap and not provide benefits.
You can be on a W2, but as soon as the contract ends, your employment ends since you're "at will" in the US.
Usually the W2 is provided through an agency and you're getting a paycheck from them while the agency is billing the company for hours at a negotiated rate, often much higher than you're being paid.
Always ask your supervisor how much they're paying for you. You might not be allowed to work for that company soon (non-competes enforced at the agency side), but you can certainly get a better idea of your value.
Most likely they're going to be prohibited from telling you. The best way to do this is to take [person] out for a round of beers. Wait until 3 beers in and see what their number is.
My belief is that 20%-30% of what you're making is a fair number.
Though if it's somewhere where you could really get a foothold and make a lot of money as an employee, 50% might be acceptable.
