It depends on the length of your cycle.
Example if you have a 28 day period, you would ovulate until the 29th March, roughly.
The best way to get a rough idea of when you will ovulate, is look at your past cycle.
Take two weeks off the date you came on your period, and that is roughly when you ovulated, so if you look at how many days that was after your period started it gives a rough indication of how many days after your last period it will take for you to next ovulate.
Also, pay close attention to your CM. It will become clearer, slippy and stretchy and you will have lots of it.
Its said that when this starts your fertile window begins, and the last day you see the CM if the day of or the day before you ovulate.
If your trying for a baby, now is the best time to start trying, so try and have sex at least every other day until you are due on.
There is no cut and dry answer to this question. It depends on the length of your cycles and when during that cycle you ovulate each month. You have to have intercourse within a small window of days of ovulating in order to have a chance of becoming pregnant. Even if you do have intercourse during that window there is still no gaurantee that the sperm will reach the egg and fertilize it. The only way to know for certain is to wait until you miss your period and take a test.