Roulette Strategy Calculator
A roulette strategy calculator turns guesswork into numbers. Before risking real money, you can estimate expected loss, how many doublings your bankroll can absorb, and how often a losing streak is likely to occur.
This page lists the formulas and shows worked examples. To run them across actual spins with strategy logic, use the Roulette Strategy Tester.
Expected loss formula
Expected loss is the part of your total wagered amount the house statistically keeps. The formula is simple:
Expected loss = Total wagered × House edge
On European roulette the house edge is 2.70%. On American roulette it is 5.26%.
| Total wagered | European (2.70%) | American (5.26%) |
|---|---|---|
| $1,000 | $27.03 | $52.63 |
| $5,000 | $135.13 | $263.15 |
| $10,000 | $270.27 | $526.31 |
| $50,000 | $1,351.35 | $2,631.57 |
Martingale absorption math
For a doubling system like Martingale, the question is how many consecutive losses your bankroll can absorb. With base bet b and bankroll B, the maximum number of losses n before you cannot place the next bet is the largest integer where:
b × (2n+1 - 1) ≤ B
Example: $10 base bet, $1,000 bankroll. After 6 losses you have wagered 10 + 20 + 40 + 80 + 160 + 320 = $630. The 7th bet would need $640. You only have $370 left. So this setup absorbs 6 losses, not 7.
Probability of N losses in a row
For an even-money bet on European roulette, the loss probability per spin is 19/37 = 51.35%. The probability of N losses in a row is (19/37)N.
| Streak length | European probability | Expected once per N spins |
|---|---|---|
| 3 losses | 13.55% | ~7 spins |
| 5 losses | 3.58% | ~28 spins |
| 7 losses | 0.94% | ~106 spins |
| 10 losses | 0.13% | ~771 spins |
| 13 losses | 0.018% | ~5,560 spins |
ROI formula
Return on investment for a session is:
ROI = (Final bankroll − Initial bankroll) / Total wagered × 100
Over many runs, the average ROI converges toward the negative house edge. Single-session ROI is noisy and not a real measure of edge.
Risk-of-ruin estimate
A rough rule for flat betting: with a unit base bet and a bankroll of K units, on a 2.70% house edge bet, your probability of ruin before doubling the bankroll is approximately:
P(ruin) ≈ 1 − ((1 − e) / (1 + e))K — where e is the house edge in decimal form.
For more exact numbers per strategy, run a batch of simulations in the tester. See Risk of Ruin for a full explanation.