If you go from hours IG time to hours IRL time, the total IC time it would cost to go through human gestation would be around 80 IRL weeks, give or take. (I did the math a few years back, I think it was 82 IRL days.)
That said, I think the easiest way to go about it would probably go from the weeks standpoint of ~40 IRL days, since that seems to be the most used. It should also be considered that elven, breed, dwarf, ect. gestation takes longer than human gestation, so you might want to add some time if you're a non-human and get knocked up.