simple formulas to calculate out and odds
You can use the simple x4 and x2 rule.
For example, if you have a flush draw, which means that you have 9 outs, at the flop (with 2 cards to come) you simply multiply 9 outs x4, and get 36% of hitting your flush. At the turn (with 1 card to come), you simply multiply 9 outs x2, and get 18% of hitting your flush.
Although this estimation is not 100% accurate, it is quite close and easy to do in real time.