progressBubble factor explained
The number that tells you how much tighter ICM makes you.
Bubble factor (BF) is the ratio between what you lose in prize equity when you lose a pot and what you gain when you win the same number of chips. In a cash game it is exactly 1. In a tournament it is almost always above 1, and that gap is the price of risking your stack.
The formula
Let L be the ICM equity you lose if you lose the chips at stake, and G the equity you gain if you win them. Then BF = L / G.
For a call that risks c chips to win w chips, the equity you need rises from the pot-odds number to:
required equity = BF · c / (BF · c + w)
With BF = 1 this is ordinary pot odds, c / (c + w). The formula treats BF as constant over the range of the bet, which is accurate enough for most decisions.
An exact example
Four players with 4000, 3000, 2000 and 1000 chips; the top three get 50%, 30% and 20%. This table shows the bubble factor of the row player when he is all-in against the column player:
| Hero \ Villain | P1 | P2 | P3 | P4 |
|---|---|---|---|---|
| Player 1 (4000) | — | 1.71 | 1.31 | 1.13 |
| Player 2 (3000) | 2.69 | — | 1.48 | 1.16 |
| Player 3 (2000) | 2.35 | 2.17 | — | 1.18 |
| Player 4 (1000) | 1.57 | 1.48 | 1.30 | — |
Now take a smaller bet. Player 3 (2000 chips) calls a 1000-chip all-in from Player 2 (3000 chips) to win 1000. For these 1000 chips the bubble factor is 1.36 (it is computed for the chips actually at stake, so it differs from the table, where the whole effective stack is at risk). Chip EV says he needs 50% equity. With this bubble factor he needs 57.6%. A hand that is a comfortable call in a cash game can be a clear fold.
What drives the number
- Stack sizes. Medium stacks facing bigger stacks have the highest BF; the chip leader against a short stack has the lowest.
- Players left until the payout jump. The closer the bubble, the larger the factor.
- The payout structure. Flat payouts (satellites) produce very large factors; winner-takes-all produces BF = 1, because the only thing that matters is chips.
How to use it
You do not need to compute it at the table. What matters is knowing the direction: on the bubble and at final tables, call ranges shrink, shove ranges against stacks that cannot afford to call grow, and you should expect to fold hands that are profitable in chip EV. The ICM calculator shows the factor for every pair of players, so you can build a feel for the numbers away from the table.
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Questions
What is a bubble factor of 1.5?
Losing the chips costs you 1.5 times as much prize equity as winning the same chips gains you, so you need clearly more equity than pot odds suggest.
Is bubble factor only for the bubble?
No. It applies at any stage where payouts make chips unequal in value, including final tables and satellites.
Why is it 1 in winner-takes-all?
Only first place pays, so equity is proportional to chips and a lost chip costs exactly what a won chip gains.
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progressGTO guides use our own solution book (v13, 8-max tournaments with ante, chip EV): an approximation of equilibrium with a modelled postflop, not an exact solution. Numbers are computed from the book and from the exact ICM model.
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