D'Alembert betting system: a slow progression on even-money bets
The D'Alembert raises your bet by one unit after every loss and lowers it by one unit after every win. It grows far slower than Martingale, but it cannot beat the house edge.
Reviewed Oct 14, 2026
Answer first
90s| Result | Next bet | Running change |
|---|---|---|
| Start | 1 unit | 0 |
| Loss | 2 units | −1 |
| Loss | 3 units | −3 |
| Win | 2 units | 0 |
| Win | 1 unit | +2 |
| Loss | 2 units | +1 |
Key numbers
D'Alembert at a glance
In short
Key takeaways
- The bet climbs one unit at a time, so a losing run hurts slowly rather than all at once.
- Equal numbers of wins and losses leave you ahead by one unit per win, which is the idea behind the system.
- Roulette greens make losses a little more common than wins, so the long-run cost is the same as flat betting.
- A single-zero wheel or a craps pass line cuts the cost of every bet the system places.
On the wheel
Where an even-money bet loses
Red bet
18 red pockets win, 20 lose on a 00 wheel
Greens
2 of 38 pockets beat red and black alike
Single-zero wheel
1 of 37 pockets; the edge drops to 2.70%
Win chance on red: 47.4% on a 00 wheel, 48.6% on a single-zero wheel.
A 10-spin session with $5 units
| Spin | Bet | Result | Session total |
|---|---|---|---|
| 1 | $5 | Win | +$5 |
| 2 | $5 | Loss | $0 |
| 3 | $10 | Loss | −$10 |
| 4 | $15 | Win | +$5 |
| 5 | $10 | Loss | −$5 |
| 6 | $15 | Loss | −$20 |
| 7 | $20 | Win | $0 |
| 8 | $15 | Win | +$15 |
| 9 | $10 | Loss | +$5 |
| 10 | $15 | Win | +$20 |
Five wins and five losses. The session ends $20 ahead, but a run of extra losses would flip it.
Why the system feels safe
The D'Alembert never doubles. After five losses in a row you bet only 6 units, where Martingale would be at 32. That is why many players see it as a calm, low-risk plan.
The cost is slower recovery. A losing run of ten spins leaves you 55 units down, and you need more wins than losses to climb back.
Sequence
Playing the D'Alembert
Step 01
Pick a small unit
A unit of 1% to 2% of your session budget leaves room for a bad run.
Step 02
Bet one unit on an even-money spot
Red, black, odd, even, 1–18 or 19–36.
Step 03
Lose: add one unit
The next bet is one unit larger.
Step 04
Win: remove one unit
Never go below one unit.
Step 05
Stop at a set point
Decide a win target and a loss limit before the first spin.
Why it cannot beat roulette
Each spin is independent and carries the same edge. The system only changes how much you bet, not your chance to win.
Over many spins, expected loss equals total money bet times the house edge. A progression usually raises the total bet, so it often raises the expected loss.
Floor rules
Terms used with the D'Alembert
Know before you sit
- Unit
- The base bet size the system adds or removes.
- Reverse D'Alembert
- Adds a unit after a win and removes one after a loss.
- Contra D'Alembert
- Another name for the reverse version.
- Flat betting
- Betting the same amount every spin.
Common mistakes
- Thinking wins and losses even out
- Equal results are not guaranteed. Greens and plain luck often leave more losses than wins, and the system needs balance to show a profit.
- Raising the unit after a bad night
- A bigger unit makes every swing bigger. It does not make the next session safer.
- Playing it on a 00 wheel
- A double-zero wheel nearly doubles the cost of every even-money bet. Look for single-zero tables when you can.
- Chasing a win target
- Pushing on to reach a fixed target after a losing run is how small losses become large ones.
Keep reading
Related pages
Go play
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Questions before and after you play
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01How it works
Where does the D'Alembert name come from?
It is named after Jean le Rond d'Alembert, an 18th-century French mathematician. He wrote about probability, but the betting system was popularized by gamblers later.
Does the D'Alembert work?
It changes the pattern of results, not the odds. On roulette, every bet still loses 5.26% on average on a 00 wheel and 2.70% on a single-zero wheel.
What is the difference between D'Alembert and Martingale?
Martingale doubles after each loss, so bets grow very fast. D'Alembert adds just one unit, so bets grow slowly and losses build up more gently.
Can I use the D'Alembert in blackjack?
You can, but blackjack doubles and splits make bet sizes uneven. Most players use it on simple even-money bets instead.
02Risk
What happens on a long losing streak?
Bets keep growing one unit at a time. After ten losses you are 55 units down and betting 11 units on the next spin.
Is the reverse D'Alembert better?
No. It changes which streaks you profit from, not the edge. It wins on hot runs and gives back on choppy ones.
What unit size should I use?
A unit of about 1% to 2% of your session money is a common choice. It leaves room for a run of losses without hitting your limit.
03Where to play
Which roulette wheel is best for the system?
A single-zero wheel. Its 2.70% edge is about half the 5.26% of a double-zero wheel, and some tables lower it further with la partage.
Is the system allowed in casinos?
Yes. Betting systems are legal everywhere; casinos only care that you follow table minimums and maximums.
Sources
- Wizard of Odds — Roulette Not from a registry (Reference source, not an official registry)The gaming industry’s standard reference for casino-game math, by actuary Michael Shackleford. Not an official registry; our calculators compute these numbers independently. · accessed Oct 14, 2026Rules, odds and house edge
- Wizard of Odds — D'Alembert Not from a registry (Reference source, not an official registry)The gaming industry’s standard reference for casino-game math, by actuary Michael Shackleford. Not an official registry; our calculators compute these numbers independently. · accessed Oct 14, 2026Rules, odds and house edge
- Nevada Gaming Control Board · accessed Oct 14, 2026Approved games and gaming revenue reports
- National Council on Problem Gambling — Help and resources Not from a registry (Reference source, not an official registry) · accessed Oct 14, 2026Free, confidential help: call or text 1-800-GAMBLER