Definition of hand improvement ratings
Hand improvement odds are the probability that you will improve your hand. You have a flush draw on the flop and want to know if you can call your opponent's bet. In this situation, you need to know the improvement odds of a hand to know if you can pay the bet in question. To do this, you need to put together the number of known cards, the hole cards, the upcoming cards and the ratio of your opponent's bet to the size of the pot.
An example
Let's go back to our colour draw above. Let's say the pot is €10. Our opponent bets €10 in 10. To put it simply, we'll say that we don't have the best hand at this stage and we need to complete our flush to win the hand. Here we know the 3 cards of the flop plus our two cards, so 5 cards out of 52. We know that 4 spades are already out (for our flush draw). This leaves 9 cards out of 47 (the unknown cards) that can help us. So, 1 time out of 5 (47/9 = 5.22 rounded up to 5) the turn will give us our flush, i.e. odds rounded up to 4:1 (1 time we hit, 4 times we don't hit). As our opponent bets 10 in 10, we will lose 4 x 10 euros, i.e. 40 euros, before making 1 x 20 euros, i.e. 20 euros. A total loss of 160 -20 or 140 euros in the long run. This is a bad call based on the odds of improving a hand.
