Ruin and Swings: Reaching a Target Before Going Broke

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Reaching a target before going broke

Starting money $

Stop when you reach $

Each bet $

Chance of winning each bet %

Load an example from the book

Ups and downs

Starting value $

Up by %

Then down by %

Times (up then down)

The doubling system

First bet $

Losses your money covers

Chance of winning each bet %

Enter your numbers, then press Calculate.

From the book, Chapter 16. Start with $20, bet $1 at a time on a fair coin, stop at $100 or nothing: you reach $100 20% of the time, after 1,600 bets on average. At the fairground wheel’s 45%, aiming for $40, it’s 1.8%. Up 50% then down 50% leaves $75 of $100; ±10% ten times leaves $90.44. Doubling from $10 needs $630 to cover six losses, goes bust 2.77% of the time and averages −$7.72 a round.

Exact arithmetic for even-money bets of a fixed size. Not gambling advice: no system beats a game with a house edge. Everything stays in your browser: no sign-up, nothing stored or sent.