# Why is it a dumb idea for me to go to a casino and play roulette ONLY until I double my money or break even?

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So I don’t gamble, and don’t ever indend to make it a habit.

But a friend told me to play roulette, and I would have a ~47% chance of doubling my money and , as long as I had enough money to keep doubling my stake, would have a ~95% break even if I kept going until I won and never played again.

So say I had \$200k in the bank and always put my money on red

Spin 1 : \$5K

Spin 2: \$10K

Spin 3: \$20K

Spin 4: \$40k

Spin 5: \$80K

Spin 6: \$160k

In this scenario, I’d have a ~47% chance of winning \$5k, and just a 2% chance of losing \$160k?

EDIT: Although just working this out, I think I would probably put the 160k into a 4% savings account if I had it, or start off way smaller amounts e.g. \$500 to reduce my chane of losing money significantly lol.

In: 8

> In this scenario, I’d have a ~47% chance of winning \$5k, and just a 2% chance of losing \$160k?

In other words, you’d have a negative expected value. Your 47% chance is +2.3k expected value, and your 2% chance is -3.2k expected value, because you lose so much more money than you’d win.

What you’re talking about is a version of something called the Martingale System. The easiest way to see a problem is to look at the exponential growth of those numbers you posted. An enormous loss is easy to accrue and you’re a person with a finite bankroll to keep doubling your bets. Another practical problem is casinos will have table limits. They aren’t going to let you double your bet forever.

Without table limits or bankroll constraints, you could potentially make money. But then, if you had infinite money why would you be wasting time on roulette?

https://en.wikipedia.org/wiki/Martingale_(betting_system)

the casino like has a limit on how big a single bet can be, if you hit the limit you are screwed

Because you don’t have infinite money. You can’t play the double bet game forever. Eventually you’ll have to stop. The risks get bigger and bigger, but the potential gain remains the same.

Watch: I have £10.

And I can make bets to get double or nothing.

So, bet 1 (betting £1) will result in me having £11 or £9.

If I lose then I go to bet 2 (betting £2), which will result in having £11 or £7.

If I lose, no worries. I try for bet 3 (betting £4), which will give me £11 or £3

If I lose again, whoops, my money is gone. Now let’s say I’m feeling great about bet 4, so I take out a loan. (Betting £8), now the potential outcomes are £11 or – £5.

Now, look at this I am plunging myself into debt. I’ve spent all my money, but I’m not fighting for a better outcome, I’m still just trying to get that single £1 coin.

Eventually, I lose enough times that I have to stop, which will be fewer attempts than you might have imagined.

The first thing is that casino tables have limits on what you can bet, so your strategy of doubling and doubling and doubling when you lose doesn’t work in the real world. But even if it did, this strategy is more likely to result in an actual loss or just breaking even after risking lots of money than it is to result in winning.

Under your example, you run out of funds after six spins. While it is unlikely to lose six spins in a row, streaks like that do happen, and if it happens to you, you are completely cleaned out.

Also, your upside is very limited compared to your downside. If you win right away, great, take your winnings and go home. But you have less than a 50% chance of that happening. What’s more likely to happen is that you lose on the first spin. Now the best you can do is break even. And there ‘s a chance that you’ll just continue to lose until you’re wiped out. So you have an under 50% chance of walking away with a relatively small amount of money compared to the amount you could lose, and once you’ve lost the first spin, the best you can hope is to break even.

And if you counter the above by saying every time you break, even you’ll just start again, that doesn’t much change the calculations, and does increase the chance of a six or more spin. Losing streak, wiping you out.

Sure, you can just make smaller bets so you can use the same pool of money and last far longer on a bad streak, but that also greatly reduces your upside. So the math stays the same.

In any event, casinos would love people who think like you to come to the roulette table all the time. There will be some winners for sure, but overall the casino wins under that strategy, as it does under all of them by the way.