This is negative progression system. In terms of its popularity it’s probably second only to the Martingale system. It actually shares some characteristics with the Martingale, as they are both negative progressions that involve increasing stake sizes after a losing bet and decreasing them after a winning bet.

This system was named after the French mathematician Jean-Baptiste le Rond d’Alembert. he D’Alembert system is commonly applied when making even money bets at the roulette table, but it can be used for pretty much any even money wager. It’s based on the theory that there should be some equilibrium with even money bets. The idea is that you should always win roughly the same number of even money bets as you lose.

It is very easy system which perhaps explains it’s popularity.

Here is quick guide.

Before you start you must decide what your base staking unit is going to be. This can be whatever you want, but we’d advise making it no more than 5% of your total bankroll. 2% is best in our opinion.
You must stake exactly one base staking unit on the first wager of any cycle when using the D’Alembert system.
After every losing wager, the stake for the following wager must increase by one base staking unit. If you started with $5, for example, then you would increase the stake to $10 if you lost. If you then lost again, you’d increase the stake to $15
After every winning wager, the stake for the following wager should decrease by one base staking unit. If a wager is won at a stake of only one unit, then it remains the same for the following wager.

The D’Alembert can help you win money in the right set of circumstances, but it can also cost you a lot of money in the wrong set of circumstances. Ultimately the exact same is true if you just bet level stakes.