Ace-to-five lowAce-to-five low is the most common method for evaluating Low handss in poker, nearly universal in American casinos, especially in High-low split games.
As in all lowball games, pairs and trips are bad: that is, any hand with no pair defeats any hand with a pair; one pair hands defeat two pair or trips, etc. No-pair hands are compared starting with the highest ranking card, just as in high poker, except that the High hand loses. In ace-to-five low, Straightss and Flusheses are ignored, and aces play as the lowest card.
For example, the hand 8-5-4-3-2 defeats 9-7-6-4-3, because eight-high is lower than nine-high. The hand 7-6-5-4-3 defeats both, because seven-high is lower still, even though it would be a straight if played for high. Aces are low, so 8-5-4-3-A defeats 8-5-4-3-2. Also, A-A-9-5-3 (a pair of aces) defeats 2-2-5-4-3 (a pair of deuces), but both of those would lose to any no-pair hand such as K-J-8-6-4. In the rare event that hands with pairs tie, kickers are used just as in high poker (but reversed): 3-3-6-4-2 defeats 3-3-6-5-A.
This is called ace-to-five low because the lowest (and therefore best) possible hand is 5-4-3-2-A, called a Wheel or "bicycle". The next best possible hand is 6-4-3-2-A, followed by 6-5-3-2-A, 6-5-4-2-A, 6-5-4-3-A, 6-5-4-3-2, 7-4-3-2-A, 7-5-3-2-1, etc.
When speaking, low hands are referred to by their highest ranking card or cards. Any nine-high hand can be called "a nine", and is defeated by any "eight". Two cards are frequently used: the hand 8-6-5-4-2 can be called "an eight-six" and will defeat "an eight-seven" such as 8-7-5-4-A.
High-low split games with ace-to-five low are usually played Cards speak, that is, without a Declaration. Frequently a qualifer is required for low (typically 8-high or 9-high). Some hands (particularly small straights and flushes) may be both the low hand and the high hand, and are particularly powerful (or particularly dangerous if they are mediocre both ways). Winning both halves of the pot in a split-pot game is called "scooping" or "hogging" the pot. The perfect hand in such a game is called a "steel wheel", 5-4-3-2-A of one suit, which plays both as perfect low and a Straight flush high. Note that it is possible--though astronomically unlikely--to have this hand and still lose money! If the pot has three players, and one other player has a mixed-suit wheel, and a third has a suited 10-9-8-7-6 for a higher straight flush, the higher straight flush wins the high half of the pot, and you and the other wheel split the low half, so you have won only a quarter of a three-way pot. Strange things can happen at poker tables.
Ace-to-five lowball is often played with a joker added to the deck. The joker always plays as the lowest card not already present in the hand (in other words, it is a Wild card): 7-5-4-Joker-A, for example, the joker plays as a 2. This can cause some interesting effects for high-low split games. Let's say that Alice has 6-5-4-3-2 (called a "straight six")--a reasonably good hand for both high and low. Burt has Joker-6-5-4-3. By applying the rule for wild cards in straights, Burt's joker plays as a 7 for high, giving him a seven-high straight to defeat Alice's six-high straight. For low, the joker plays as an ace--the lowest card not in Burt's hand--and his hand also defeats Alice for low, because his low hand is 6-5-4-3-A, lower than her straight six by one notch. Jokers are very powerful in high-low split games.