It all varies. For example, at Comair we have a line gaurantee of 82-92 hrs/mo. If you don't drop anything for the month, then you are gauranteed at least the line value you were awarded. It's very easy to get paid a lot more because of delays, displacements, etc. It's also easy to fly a lot less (i.e. displaced with no re-assignment) and still get paid your line value.
A 2nd yr FO making 35.75/hr with a min line value of 82hrs/mo will make 35178/yr. If you factor in per diem at a modest 280hrs/month and 1.65/hr you add another 5544 bringing it up to 40788. Also, don't forget, depending on your anniversary date, you may get up to two raises during the calendar year (1 contractual on the contract anniversary and the other on your YOS anniversary).
If you want to keep it simple, though, just find out the min line value at the respective carrier and multiply it by the # of bid periods per year (+ per diem if you want).