Lesson 10 · Advanced concepts · 5 min
Expected value and strategy cost
How decisions are compared, and why the correct action is not about one outcome.
Decisions are compared by expected value
Expected value (EV) is the average result of a decision if you could repeat the exact same situation forever. Hitting hard 16 against a ten will often bust — but evaluated over every possible next card and every dealer outcome, hitting loses less per wager than standing. EV is the number that makes that comparison precise, and every basic-strategy cell is simply the action with the highest EV for that state.
This is why “correct” never means “will win.” The correct action is the one that wins the most or loses the least on average. A cell can be correct and still lose the majority of the time — hard 16 against a ten is exactly that.
Where strategy numbers come from
The EV of each action is computed from the full probability tree beneath a decision: every card you could draw, every card the dealer could hold and draw, with the table’s rules applied at each step — H17 or S17, DAS or not, peek or ENHC. Charts are then verified cell-by-cell against independent published references before this site calls them verified.
Change the rules and parts of the tree change: the dealer’s soft-17 draw rule alone moves the comparison enough to flip real cells, which is why the trainer keeps a separate verified chart per rules profile.
Why this site says “correct action” — not an exact cost
You will notice the trainer grades decisions as correct or incorrect and shows the preferred action and its fallback, but does not yet quote “this mistake cost you 0.14 units.” Exact per-action EV values are a separate verification problem from the action label: the number must be computed for the exact rules profile, under a stated calculation convention, and checked against a matched reference.
Until that work clears verification, the site deliberately withholds precise costs rather than publish approximate ones. Rule effects interact, and rounded numbers borrowed from a different rule set would be false precision. What you can trust today: the action label itself is verified, and recurring mistakes surface in Review and Statistics even without a unit figure attached.
Strategy cost
“Strategy cost” is the EV you give up by deviating from the correct action — standing on 16 against a 7 instead of hitting, insuring a natural, mis-splitting 5s. Single deviations look tiny; repeated across hundreds of decisions they are exactly the difference between playing a tight game and donating extra edge to the house.
That framing is the point of the whole trainer: not to win any particular hand, but to drive avoidable strategy cost toward zero.
Practice this
See exactly how charts are sourced, cross-checked, and locked before a profile becomes practice-enabled.
Read the methodology