True count, explained

The formula

true count = running count / decks remaining

The running count is the number you keep in your head as cards come out. The decks remaining is your estimate of what is still in the shoe, including the cards in the discard tray. A six-deck shoe with three decks visible in the discard tray has three decks remaining. The true count is the running count divided by that estimate.

Why divide at all? A plus six running count means six more small cards have come out than tens. If the shoe still has five decks left, those six extra small cards are diluted across a lot of unseen cardboard. If there is only one deck left, the same six imbalance means the remaining deck is dramatically rich in tens. The true count normalises for that depth so the bet ramp can key off a single number that means the same thing in any spot.

Half-deck rounding

At a real table you do not have time to do long division on fractional decks. The convention every professional uses is half-deck rounding. Estimate decks remaining in increments of one half. Most counters glance at the discard tray and call it: two decks, two and a half, three. With practice the estimate becomes automatic.

Stack21 mirrors this exactly. The post-round reveal divides by your half-deck estimate, not by an internal floating-point value the engine could compute precisely. We do this on purpose. Practicing against an oracle that uses information you would not have at the table is a bad habit; it would let you sneak by with rough estimates that fail in real conditions. The same calculation lives in the true count calculator if you want to sanity-check spot conversions.

What true count values mean

Each plus one of true count adds roughly half a percent of advantage to the player. The neutral point — where the basic-strategy player and the house break even on expected value — is around true count plus one on a typical six-deck S17 game.

• True count zero or below: bet the minimum.
• True count plus one: bet one or two units. The edge is small. Most counters do not vary much here.
• True count plus two: the edge is real. Two to four units depending on the ramp.
• True count plus three: insurance becomes correct. Bet ramps step up.
• True count plus four and higher: the most profitable spots in the shoe. Top of the ramp.

The two mistakes that kill accuracy

The first mistake is forgetting to convert. New counters keep a clean running count and then bet on the raw running count value, which is meaningless without a depth correction. The cheapest fix is to make a habit of converting at every dealer shuffle pause: glance at the tray, do the division, lock in the true count for the next round.

The second is rounding aggressively in your own favour. If the running count is plus four and there are about three decks left, the true count is plus one point three, which rounds to plus one or plus one and a half. It is not plus two. Calling it plus two so you can bet up is the single most common way amateur counters give back their edge. The discipline of treating the half-deck floor as the floor — not as a number you negotiate with — is what separates a counter who clears the door from one who does not.