N0 / SCORE Calculator

N0 is the most honest single number for evaluating an advantage-play system. It tells you how many rounds you need to play before your edge starts to dominate variance — the lower your N0, the faster the system 'pays off' in real terms.

N0 · Marginal

19,600rounds

Consider bumping spread or system selectivity.

≈ 245 hours of play at 80 rounds/hr.

What N0 is

N0 = variance / edge². It's the number of rounds at which one standard deviation of bankroll swing equals the cumulative expected win. Below N0, variance dominates. Above N0, your edge starts dominating.

Hi-Lo at typical advantage-play parameters has N0 ≈ 13,000 rounds — about 160 hours of play before the math has spoken.

Why N0 ranks systems honestly

A counting system with a 1% edge but σ=2.0 has the same N0 as a system with a 0.5% edge and σ=1.0. The two systems are equally efficient per round even though their headline edges differ. N0 strips out the noise.

SCORE — the dollar version

SCORE = (annual win at $1 unit bet)² / variance. Same idea as N0, normalized to dollars per year per dollar of bankroll. Schlesinger pioneered SCORE as the AP community's standard ranking metric. The math underneath is identical.

How to use it

FAQ

What's a good N0?

For modern blackjack counting at typical spreads, anything below 15,000 is competitive. Below 10,000 is excellent. Above 25,000 means the system isn't worth the effort vs simpler alternatives.

How is N0 different from RoR?

RoR tells you the probability of busting; N0 tells you when the expected win starts to dominate variance. Both depend on edge and variance, but they answer different questions.

Does N0 account for camouflage / cover plays?

No. Pure-math N0 assumes optimal play. Real-world cover plays raise the effective N0 because you give back some edge for stealth. Some APs estimate 'practical N0' at 1.3-1.5× the math N0.

Is N0 the same as SCORE?

They're different units of the same idea. N0 is in rounds, SCORE is in dollars per year per $10k bankroll. Both rank systems by risk-adjusted return; pick whichever feels more intuitive.

How does spread affect N0?

Bigger spread raises both edge (good) and variance (bad). Whether N0 improves depends on the rules and penetration. Most published spreads (1-12 to 1-20) are tuned for near-optimal N0.

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Last updated 2026-05-06. Spot an error?