Learn / Penetration

Penetration is the share of the shoe that is dealt before it is shuffled.

It is usually marked by a cut card. The same ratio also describes how far a shoe has progressed at any moment.

Definition

Cards dealt divided by the cards in the full shoe.

Penetration = cards dealt before the shuffle ÷ cards in the full shoe. A standard deck has 52 cards, so an 8-deck shoe holds 416 cards and a 6-deck shoe 312.

Shoe Cards in the shoe Cards dealt before the shuffle Penetration
8 decks 416 208 208 ÷ 416 = 50%
8 decks 416 312 312 ÷ 416 = 75%
6 decks 312 234 234 ÷ 312 = 75%
6 decks 312 260 260 ÷ 312 ≈ 83.3%

The same percentage can mean a different number of cards: 75% is 312 cards in an 8-deck shoe and 234 in a 6-deck shoe.

Cards and decks remaining

How far into the shoe, and how much is left.

At any moment, the cards remaining are the cards in the full shoe minus the cards already dealt. Dividing by 52 gives the decks remaining — the divisor of the True Count.

8 decks, 300 dealt → 416 − 300 = 116 cards remaining
Decks remaining → 116 ÷ 52 ≈ 2.23 decks
Shoe dealt so far → 300 ÷ 416 ≈ 72.1%
Running Count +4 → True Count = +4 ÷ 2.23 ≈ +1.79
What penetration changes — and what it does not

Deeper penetration means more rounds from a depleted shoe. It does not guarantee an advantage.

As more of the shoe is dealt, the remaining composition can move further from the starting shoe — in either direction.

Depth
More Depleted Shoes
With deeper penetration, more rounds are dealt from shoes whose composition differs more from the starting shoe.
Both directions
Not Only Favourable
The remaining composition can become less favourable as well as more favourable for the player.
No guarantee
No Assured Edge or Profit
Higher penetration does not make any round positive and does not guarantee an advantage or a profit.
Context
Rules and Play Matter
Any effect also depends on the rules, the playing decisions, the betting and the number of rounds played.
How OOB treats late-shoe states.
OOB calculates action EVs from the recorded remaining shoe at any depth. The pre-bet EV estimate used for the suggested initial bet is calibrated only within a defined domain (at least 104 cards remaining and a ten-card density between 26% and 34%); outside it the uncalibrated value is used. See Expected Value and the Methodology.

The published One Million Cards tracks and the 100-Hour Simulated Replay use an 8-deck shoe dealt to a cut card at 208 of 416 cards (50% penetration). Their results do not describe other penetrations.

Continue

Related pages and published evidence.

True Count vs Exact Composition
What a count summarises and what the full composition keeps.
Read the Page →
Expected Value
Action EV, the pre-bet estimate and the realised result.
Read the Page →
One Million Cards
A retrospective comparison on simulated tracks at 50% penetration.
See the Comparison →