Deviations

What Are Deviations?

Basic strategy is optimal when you don't know the composition of the remaining cards. But a card counter does know — the true count tells you whether the shoe is rich in high or low cards. At certain counts, a different action becomes better than the basic strategy play. These are called deviations.

Each deviation has an index number and two actions. You play the first action when the true count is below the index, and the second action when the true count is at or above the index. For example, Hard 16 vs 10 has an index of +0 with Hit → Stand. That means: hit when the TC is below 0, and stand when the TC is 0 or higher.

EV vs True Count Explorer

This is the core visualization. Select a hand and see how the expected value of each action changes across true counts. Where the lines cross is the exact point where the optimal action switches — that crossing is the deviation threshold.

How Many Deviations Do You Need?

Deviations are ranked by EV gain. The first few deviations capture most of the available edge, with sharply diminishing returns after that. The famous “Illustrious 18” captures the lion's share of deviation value. The chart below shows the cumulative EV gain as you add deviations in order of importance.

The Illustrious 18

The 18 most valuable deviations for the standard 6-deck shoe, ranked by EV impact. These are the ones worth memorizing.