Bankroll Sizing Calculator

Most bankroll advice is rules of thumb. This calculator works the formula in reverse — pick your acceptable risk of ruin and your edge, and it tells you the minimum bankroll required to play at a given unit bet. Use it to size up for pro play or to know when your trip bankroll is too thin.

Target risk of ruin

Unit bet ($)

Edge %

Std deviation (σ)

Minimum bankroll

$12,953

518× the unit bet at 1% RoR. Treat this as a floor — add 20-30% margin for camouflage and edge mis-estimation.

The math, inverted

Risk of ruin RoR = e^(−2 × edge × bankroll / (σ² × bet)). Solving for bankroll:

bankroll = − ln(RoR) × σ² × bet / (2 × edge)

Plug in your target RoR (e.g., 0.01 for 1%), edge as a fraction, σ per unit bet, and unit bet — get the minimum starting bankroll.

Common targets

1% RoR (professional standard) — sustainable indefinitely; what serious APs target
5% RoR (aggressive trip play) — acceptable for short-term goals
13.5% RoR (full Kelly) — maximizes growth, accepts the risk of busting once in 7 careers
0.1% RoR (ultra-conservative) — for risk-averse players or early-career APs building a roll

What this doesn't include

The formula assumes constant edge and constant bet. Real spread play (counting) has edge varying by true count — your effective bet for the formula is a weighted average across counts. The result is an approximation; treat it as a floor, not a precise number.

Practical anchors

1% AP edge, σ=1.5, $25 unit bet → $25,000 bankroll for 1% RoR
1% AP edge, σ=1.5, $5 unit bet → $5,000 for 1% RoR (pro entry-level)
1% AP edge, σ=1.5, $25 unit bet → $11,000 for 5% RoR (trip play)
Half the edge → 4× the bankroll for the same RoR (variance squares)

FAQ

What RoR should I target?

Professionals target 1% RoR. Trip players accept 5%. Full Kelly sits at 13.5% RoR — high growth, high drawdown. Below 0.1% is ultra-conservative bankroll preservation.

How does halving the edge affect bankroll requirements?

Bankroll scales as σ²/edge — so halving the edge requires roughly 2× the bankroll for the same RoR (or 4× if variance grows too). Edge mis-estimation is brutal at the bankroll-sizing layer.

Does the formula work for negative-edge games?

No. With no positive edge, bust is certain over enough time — there's no minimum bankroll that sustains play. The formula returns garbage values for negative inputs.

Should I size for the worst case?

Size for your worst realistic case, not the absolute worst. A 0.1% RoR is overkill — you'll never use the deep tail. 1% balances safety with capital efficiency.

Is the result a hard floor?

It's an approximate floor. Real-world variance from cover plays, casino heat, and edge mis-estimation pushes practical bankroll requirements 20-30% above the formula. Treat the calculator's output as a minimum starting point.

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

Bankroll Sizing Calculator

The math, inverted

Common targets

What this doesn't include

Practical anchors

FAQ

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