Wagering and Bankroll play an important roll in card counting. First, a card counter knows he must raise his bet when the odds are in his favor. Second, a counter must have a large enough bankroll to weather a losing streak. Remember a statistical advantage is only evident in the long term. Short term you can lose and often do.
Your bankroll is the starting amount of money you sit down to play blackjack with. Typically, the minimum bet (and therefore the maximum bet) is determined by the bankroll. Again, you must have sufficient funds to continue through a losing streak.
An average minimum wager is your total bankroll divided by 150. Thus a $ 3000 bankroll would indicate a $ 20 minimum bet. This is just less than 1% of the bankroll. For slightly more aggressive wager, set the minimum to 1%. Thus $ 3000 bankroll yields a $ 30 minimum bet.
A card counter must increase his wager when the odds favor him. When the odds are not in his favor, he wagers the minimum bet (or leaves the table). In a typical 5 deck shoe, a wager of 8 times the minimum bet is recommended. You must wager enough to recuperate the losses sustained while betting the table minimum. I personally like to see a 10 times increase. So if your minimum bet is $ 20, your maximum should be $ 200.
Another common wagering tactic is to bet proportional to the count. For example, you would want to wager more on a +5 count versus a +1 count. You can use the table below as a guide to staggering the high wager. Note that the amount you increase from the minimum wager depends on the number of decks used.
Count 1 Deck 2 Decks Shoe
------ ------ ------- ----
It is important to note that casino spot card counters by watching the bet spread. A casino will count cards of a suspect player and note if he is wagering more on positive counts. If the player is identified as a counter, the dealer will be instructed to shuffle very frequently, constantly resetting the running count and preventing the player for reaching an advantage. Keep this is mind when wagering, and know that large jumps in the wager are a signal to the casino.