When comparing pot odds to my drawing odds I've always worked out my odds of hitting a draw on the turn compared to the pot odds. Is this correct, or should I compare my odds of hitting it by the river. If I go by the latter, wouldn't I have to include the bet i'd be making on the turn as well to see the river?

For example say I have a flush draw on the flop. I have odds of about 4-1 of hitting it on the turn, and about 2-1 for hitting it by the river. The pot is about $.75 in a .25/.50 limit game. My pot odds are about 3-1. Now do I compare the pot odds to the 4-1 odds of hitting it on the turn, or do I compare them to the 2-1 odds of hitting it by the river?

Cheers.