Every time you face a bet with a drawing hand, you're making a math decision. Get it right and you make money over time; get it wrong and you leak chips every session. Pot odds and outs are the two numbers you need.
Step 1: Count your outs
An out is a card that will improve your hand to what is probably the best hand. Common draws:
- Flush draw: 9 outs (13 cards of a suit minus the 4 you can see)
- Open-ended straight draw: 8 outs
- Gutshot straight draw: 4 outs
- Flush draw + open-ended straight draw: 15 outs
Be careful with "dirty" outs — cards that complete your hand but also give your opponent a better one.
Step 2: Turn outs into equity
The rule of 2 and 4 is a quick shortcut: multiply your outs by 2 for one card to come, or by 4 when you'll see both the turn and river (for example, when all-in on the flop). A flush draw on the flop is roughly 9 × 4 = 36% to hit by the river; the exact figure is 35%.
Step 3: Work out the pot odds
Pot odds compare what you must call with what you can win. The equity you need to call is:
Call ÷ (Pot including the bet + Call)
If the pot is $100 and your opponent bets $50, the pot is $150 and you must call $50. You need $50 ÷ $200 = 25% equity.
Step 4: Compare
If your equity is higher than the equity you need, calling is profitable. In the example above, a flush draw with one card to come has about 19% — not quite enough on its own. If you're all-in and will see both cards, you have 35% and it's an easy call.
Implied odds
When you're not all-in, you can often win more money on later streets when you hit. These are implied odds. In the example, you would need to win about $61 more on average when you hit to make the call break even. Against an opponent who pays off big bets, that's realistic; against a cautious player, it may not be.
Practice with a calculator
Try different spots in the free pot odds calculator, check exact equities in the poker odds calculator, and see the dollar value of each decision with the EV calculator.