Poker is a game in which the players place bets in succession till the hand is won by one of them. There are different rules governing the quantum of these bets and these rules are referred to as betting structures. The betting structures commonly used are fixed limit online poker, pot limit and no limit.
Fixed limit games are also referred to as limit games. In fixed limit games the quantum of the call and the raise is governed by the table stakes and the player only decides whether he should call or raise or fold. For example if the table stakes are $10/$20 then the unit of the raise is $10 in the lower rounds and $20 in the higher rounds.
Another feature of fixed limit games is that there is a cap on the number of raises allowed in a particular round. This is fixed by the casino and is usually three or four. The concept of fixed limit betting structure can be illustrated by the following example of a $10/$20 game with a limit of three raises per round. It is a lower round so the unit is $10.
Player 1 starts the betting with $10. Player 2 raises and hence wagers $20 ($10 for the call and $10 for the first raise). The call is now $20. Player 3 raises and hence wagers $30 ($20 for the call and $10 for the second raise). The call is now $30. The betting is back to Player 1, who raises and hence wagers $40 ($30 for the call and $10 for the third raise). The call is now $40. Now no more raises are allowed and the betting will continue at the call amount of $40.
The rule for pot limit games is that the raise cannot exceed the amount in the pot before the raise but after the call. The calculation of the raise is a bit more difficult and is illustrated below. As in the previous example Player1 starts the betting with $10. The call is now $10. Player2 first has to wager the call. Therefore he puts $10 in the pot making the pot amount $20. He can now raise by $20 and puts another $20 in the pot. The amount in the pot is now $40 and the call amount for the next player is $30.
Player 3 has to first make the call and he puts $30 in the pot. The amount in the pot increases to $70. Player3 can raise maximum by $70. He may choose to raise by a lower amount. If he raises by $50 the amount in the pot increases to $120 and the call is now $80. Player1 has to first put $80 in the pot for the call, making the pot amount $200. He can now raise by maximum of $200. Hence in pot limit games both the call and the pot increase at a much faster rate.
In the no limit betting structure there is no limit on the raise and therefore no calculations required but the betting increases at a much faster pace than even in the pot limit structure.