Ø Subtract cards in discard tray – The most common method is to look at the discard tray and subtract from the starting number of decks. Of course, this is not quite accurate for playing decisions since it ignores the cards on the table.
Ø Subtract cards dealt – In calculating the remaining cards, subtract the total number of cards dealt from the total cards including those on the table both seen and unseen. This is a bit more accurate, and more difficult. (Many Blackjack simulators incorrectly use this method.)
Ø Subtract cards seen – Only take into account the actual number of cards seen, that is, the cards in the discard tray (minus unseen burn cards) plus only the cards on the table that you have seen. This is the most accurate and the most difficult. Few people use this method.
Ø Count hands – In single-deck games, some people count the number of hands, multiply by 2.7 and subtract from 52.
By far, most people look at the discard tray.
How closely must we estimate remaining decks?
That is, what is the resolution of the estimate? Very few people estimate remaining cards to the exact card. (Although some Blackjack simulators inaccurately assume this.) When playing shoes, most people estimate to the nearest remaining full-decks or half-decks. When playing single-deck, you should estimate by quarter-decks. In deeply dealt games, you might want to be more accurate toward the end of the shoe. Alas, we see few deeply dealt Blackjack games these days. For best results, you should estimate the remaining decks to the same degree of accuracy that was used during generation of the indexes that you are using.
Custom true count calculation
Some people use a table of divisors (or multipliers) instead of dividing by the remaining decks. For example, the Mentor count uses a table of multipliers to convert the running count to a true count depending on a table of remaining decks that becomes more precise as the shoe is depleted. This is described in Blackjack Bluebook II by Fred Renzey.
© 2009 Norman Wattenberger
