Sex Calculator?

Some things you can work out, like when a baby will be born, but if you mean sex as in gender then no, it doesn't work that way in humans. It does with some reptiles, though. Gender is down to the heat of the eggs (and so, to an extent, the time of year).

For humans, average gestation period is 283.4 days (which I only know because my friend is 8 months pregnant and we were having fun trying to work out what she was doing the day she conceived). I'm sure you can probably find a version of this on the web.