If your talking about online play (assumed) I use an online odds calculator which displays the draw odds, pot oods, and outs.

Prior to the flop all I know is the strength of the hand I was delt. Once the flop is on board I have the draw odds displayed for turn to river and naturally they go down after the turn card is revealed and it is not allways 1/2 the odds for turn to river.

I am not sure if I really understood your question as well but this is how I handle the online games.