Flat betting is the default that progression systems are sold against, and it is the better default. Since each bet is independent, changing size based on previous results cannot change expectation.
What it can change is risk. Raising bets after losses concentrates exposure into the worst sequences; raising after wins concentrates it into the best ones. Flat betting spreads it evenly, which is why a bankroll lasts more predictably.
The only situations where varying bet size is mathematically justified are ones where the edge itself changes, such as counting cards in blackjack. Absent that, the size of your last bet contains no information about the next one.
Flat betting is also the only approach that keeps a session's cost predictable in advance. If you know the unit, the house edge and roughly how many bets an hour the game deals, the expected cost of an evening is arithmetic rather than a hope. Progressions make that calculation impossible, which is part of their appeal and all of their problem.
Related terms in odds & money
- House edge — The average share of each bet the casino expects to keep over the long run.
- RTP — Return to player: the mirror of house edge, quoted as what comes back rather than what is kept.
- Expected value — The average result of a bet if it could be repeated indefinitely.
- Variance — How widely results scatter around their expected value.
- Standard deviation — A measure of how far results typically stray from the average.
- Bankroll — The money set aside for gambling, kept separate from money needed for anything else.
Where an entry quotes a number, that figure comes from the computed sections of this site rather than from another glossary, so the definition and the derivation cannot drift apart. Each entry links to the page where the number is worked out.