Bankroll calculator

Why bankroll management is the only edge you control

The house edge in casino games is fixed. You cannot beat it through bet sizing, betting systems (Martingale, Fibonacci, D'Alembert), pattern recognition, or willpower. What you can control is how long your money lasts and how steep the variance feels.

Bankroll management is the discipline of choosing bet sizes proportional to your total roll. The smaller each bet relative to your bankroll, the lower your risk of ruin — the probability that you lose everything before variance smooths out. Risk of ruin is a real, calculable quantity, and proper bankroll sizing pushes it toward zero.

Practical rules that work

Three rules cover 90% of the value:

1. Bet size ≤ 1% of bankroll for negative-EV games. A $1,000 bankroll allows $10 max per bet. This gives roughly 100 bets of survival assuming you lose every one — which never happens, so practical lifespan is much longer.
2. Bet size ≤ 5% Kelly for positive-EV bets. If you genuinely have an edge (sports betting with strong models, advantage play), use the Kelly criterion with a 0.25× to 0.5× safety multiplier.
3. Define a session unit and a stop-loss. A "session unit" is the amount you'll spend in one sitting. A stop-loss is the point at which you walk away. Both should be decided before you start, not in the heat of play.

Risk of ruin — the math

For a flat-betting game with house edge h and bet size b against bankroll B, risk of ruin can be approximated as:

P(ruin) ≈ ((1 - h) / (1 + h))^(B/b)

For a 1% house edge game with $100 bets and a $1000 bankroll, P(ruin) is roughly 81%. Drop bet size to $20 (5% of bankroll) and P(ruin) falls to ~37%. Drop to $10 (1%) and it's ~17%. Each halving of the bet ratio doesn't quite halve risk of ruin — but it dramatically extends average session length.

Working example

A player with a $2,000 disposable bankroll wants to play 30 weekly sessions before reassessing. That's $66 per session. At $1 bets, that's 66 spins per session — too few to feel meaningful, but not enough variance to bust often. At $0.50 bets, 132 spins. At $0.20 bets, 330 spins — proper recreational pace.

The calculator above runs this math live: enter total bankroll, intended sessions, and risk-per-bet percentage, and it returns a recommended unit bet plus expected loss per session at your chosen RTP. Use it to set realistic expectations before any session starts.

A warning about doubling-down systems

Martingale, Fibonacci, Labouchere, and other progressive betting systems all share one feature: they hide variance behind a streak of small wins, then deliver one catastrophic loss that wipes out hours of gains. Mathematically they convert a series of small expected losses into one large expected loss — net EV unchanged, but with a much higher risk of ruin per session.

Tables and slots have bet caps. Whatever ceiling you imagine doubling toward, the table has it lower. Eight consecutive black wheel spins on roulette is roughly a 1-in-256 event — improbable but not vanishingly rare. After eight doublings from a $1 base bet you'd need to wager $256 just to recover the original $1. This is not a strategy; it is a high-variance way to lose the same money.