Bubble factor calculator (ICM bubble factor + risk premium)
Bubble factor measures tournament ICM pressure: it equals the cash-equity ($EV) you lose per chip risked divided by the $EV you gain per chip won, under ICM. A bubble factor of 1 means no bubble pressure (e.g. winner-take-all, where $EV is linear in chips); above 1 means losing hurts more than winning helps. Example: 4-handed with 3 pay spots (50/30/20), a 1,500 short stack against an 8,000 big stack has a bubble factor of about 1.41 — meaning you need about 8.4 points of equity more than the 50% chip-EV break-even (an ICM break-even near 58.4%) to call off for your tournament life. All figures are computed by lib/bubble-factor.ts reusing a deterministic ICM engine (Malmuth-Harville).
Methodology
All figures are computed deterministically by lib/bubble-factor.ts, reusing icmEquities (the Malmuth-Harville Independent Chip Model) from lib/poker-math.ts; the LLM generates no numbers. Steps: chips at risk c = min(hero stack, villain stack); ICM gives hero's cash expectation in three chip distributions — now, after winning c (hero +c, villain −c), and after losing c (hero −c, villain +c); ΔW = win − now, ΔL = now − lose; bubble factor = (ΔL / chips) ÷ (ΔW / chips) = ΔL/ΔW (chips won and lost are equal, so normalising by chips leaves it unchanged). The risk premium is derived from the bubble factor: the break-even win rate for a symmetric all-in is BF/(1+BF), chip-EV break-even is 50%, and their difference (BF−1)/(2(1+BF)) is the extra equity required. All three branches' $equity come from the same ICM engine, so they reconcile digit-for-digit with our ICM calculator.
Full methodology and math sources
For educational and study use only; not betting advice. This site offers no real-money play and no real-time in-game assistance.
FAQ
What is a bubble factor?
The bubble factor quantifies tournament ICM pressure: under the Independent Chip Model it equals the cash-equity you lose per chip risked divided by the cash-equity you gain per chip won. Because big stacks have diminishing marginal value, the loss usually exceeds the gain, so the bubble factor is at least 1; the closer to the money bubble and the steeper the payouts, the higher it climbs. It was introduced by Arnold Snyder in Tournament Poker for Advanced Players.
What is the bubble factor for a short stack vs a big stack 4-handed with 3 paid?
With stacks 8000 / 5500 / 5000 / 1500 and payouts 50/30/20, the short stack (1,500) versus the big stack (8,000) has a bubble factor of about 1.41. The risk premium: chip-EV break-even is 50% and the ICM break-even is about 58.4%, so you need about 8.4 points of equity more than chip-EV to call off for your tournament life. The reverse (big vs short) is lower (about 1.09) — the bubble factor is directional, and the short stack bears more pressure.
How do I use the risk premium?
The risk premium is the extra win rate required because of ICM. Without ICM a symmetric all-in breaks even at 50%; under bubble pressure the break-even rises to BF/(1+BF). Their difference, (BF−1)/(2(1+BF)), is the risk premium. For a bubble factor of 2 you need 66.7% (an extra +16.7 points). Add it to your chip-EV calling threshold to get the true, ICM-adjusted standard.
How are the numbers trustworthy?
The cash expectations for all three branches (now / win / lose) are computed by the same deterministic ICM engine, icmEquities (Malmuth-Harville), and reconcile digit-for-digit with our ICM calculator — a same-source cross-check. Every number is produced by pure, reproducible code, never by AI. Under winner-take-all the bubble factor is exactly 1 ($EV is linear in chips), a natural correctness anchor.