Deviations

Deviations are changes from basic strategy when TC reaches a specific threshold. The Illustrious 18 are among the most valuable Hi-Lo index plays.

Implementation Assumptions

The app uses the TC shown on screen. A deviation applies only when TC reaches the table threshold; otherwise it falls back to basic strategy.

Illustrious 18

Situation	Threshold	Deviation
Insurance	TC >= +3	Take Insurance
16 vs 10	TC >= 0	Stand if surrender is unavailable
15 vs 10	TC >= +4	Stand if surrender is unavailable
10 vs 10	TC >= +4	Double
16 vs 9	TC >= +5	Stand
13 vs 2	TC >= -1	Stand
13 vs 3	TC >= -2	Stand
12 vs 2	TC >= +3	Stand
12 vs 3	TC >= +2	Stand
11 vs A	TC >= +1	Double
10 vs A	TC >= +4	Double
9 vs 2	TC >= +1	Double
9 vs 7	TC >= +3	Double
10,10 vs 5	TC >= +5	Split
10,10 vs 6	TC >= +4	Split
12 vs 4	TC < 0	Hit
12 vs 5	TC < -2	Hit
12 vs 6	TC < -1	Hit

Fab 4

Fab 4 refers to four important late-surrender index plays in Hi-Lo.

Situation	Threshold	Deviation
15 vs 10	Basic Strategy R	Surrender
15 vs A	H17 +1 / S17 +2	Surrender
15 vs 9	TC >= +2	Surrender
14 vs 10	TC >= +3	Surrender

Insurance EV and Variance

Insurance is essentially a bet that the dealer's hole card is a 10-value card. Because it pays 2:1, insurance is worth taking only when the remaining shoe has enough 10-value cards to pass the break-even point. This is why Hi-Lo commonly uses TC >= +3 as the insurance index.

Over the long run, the main value of taking insurance correctly is increasing EV: at high TC, this side bet can move from negative expectation in normal situations to positive expectation for the player.

Insurance also affects variance. It can offset the main-bet loss when the dealer has blackjack, especially because high TC often comes with larger bets, so it can make the result distribution smoother and reduce the downside impact of a large bet running into dealer blackjack. However, insurance is still an additional side bet, so the more precise interpretation is: correct insurance mainly improves EV, while it may smooth variance in some high-risk situations, rather than guaranteeing lower variance under every statistical view.

The simulation below uses Hi-Lo with a 4/8/12/16/20 Bet Ramp over 500000 runs, with the threshold set at TC > 3.

Seat 1 500000-run simulation using Hi-Lo, Bet Ramp 4/8/12/16/20, with insurance — Seat 1: with insurance

Seat 2 500000-run simulation using Hi-Lo, Bet Ramp 4/8/12/16/20, without insurance — Seat 2: without insurance

From the charts above, Seat 1 with insurance achieves a higher overall ROI (0.93% vs. 0.64%) and higher EV / 100 (31.76 vs. 21.48), while SD / 100 is nearly the same (581.56 vs. 582.50). This matches the idea above: correct insurance mainly improves EV, while it may slightly smooth the volatility of high-TC, large-bet situations when the dealer has blackjack.