M-Ratio Calculator (Harrington Zones)

Knowing which gear you're in

The M-ratio is the single number that tells you how long you can survive tournament play without winning another chip. It answers a more useful question than "how many chips do I have?" because chip count without context is meaningless; what matters is how many orbits you can afford to wait. Dan Harrington popularised the concept in his tournament strategy books, and the five zones he defined remain the clearest framework for thinking about stack depth in MTTs.

The formula

M = stack / (SB + BB + antes_per_orbit)

where antes_per_orbit is the total antes paid by all players in one full round of the table. At a 9-handed table with a $100 big blind ante, antes_per_orbit = $100 (since the BB-ante model has only one ante per orbit regardless of player count). At a traditional-ante structure with $25 antes and 8 non-dealer players posting, antes_per_orbit = $200.

Example: 9-handed table, 25/50 blinds with a 50bb ante (modern structure). Orbit cost = 25 + 50 + 50 = $125. Stack = 2,500. M = 2,500 / 125 = 20.

The five zones

• Green (M > 20): Full flexibility. Play your normal game with no stack-depth-driven urgency.
• Yellow (M = 10-20): Some pressure. Open-limping and speculative calls lose value. Widen shove ranges; standard 3-bet-fold ranges become costlier.
• Orange (M = 6-10): Significant pressure. Prefer open-shoves to standard raises. Speculative hands (suited connectors, small pairs) need more justification.
• Red (M = 1-6): Emergency mode. The correct strategy is to find the best spot to get all-in; almost any reasonable hand from late position is a shove candidate. See the pushbot trainer for Nash shove ranges by stack depth.
• Dead (M < 1): You have less than one orbit left. Any hand, any position with fold equity is a shove. You need to gamble.

Worked example

Late in a tournament. Blinds 500/1,000 with a 1,000 BB ante at a 9-handed table. Orbit cost: 500 + 1,000 + 1,000 = 2,500. Player has 18,000 chips: M = 18,000 / 2,500 = 7.2. That's Orange zone, not Yellow as a player might intuitively feel with 18 big blinds. The orbit cost from antes makes the effective pressure higher than raw BB count suggests.

Now the same player at a 5-handed table (late in the tournament, two tables left). Orbit cost at 5-handed with a BB-ante: 500 + 1,000 + 1,000 = 2,500 (BB-ante doesn't change with player count). But Harrington's Effective M adjusts for short-handed play: Effective M = M * (players at table / full table size) = 7.2 * (5/9) = 4.0. Deep into Red zone. The same chip stack that felt like Yellow thinking has a full-table M of 7.2, but only 4.0 effective M for strategy purposes.

What each output means

M-ratio is the raw orbit count. Effective M adjusts for short-handed play. Zone classification maps the number to a strategic gear. Action recommendation translates the zone into a one-line strategic orientation: play for stacks, widen shoves, emergency shove mode. Orbit cost breakdown shows exactly how antes, blinds, and table size combine to produce the orbit cost, which is frequently surprising to players who only think in terms of big blind counts.

Where the model breaks

M-ratio is a snapshot, not a trajectory. A player with M = 15 at 100/200 blinds is in very different shape than a player with M = 15 at 5,000/10,000 blinds, because the blind structure's escalation rate determines how fast M will fall. Rapid blind levels that double every 10 minutes shrink M much faster than slow structures, and the calculator doesn't model future blind escalation.

The zones are strategic guides, not mechanical rules. A player in Yellow zone with a big stack of high-equity hands facing weak opposition should play differently than a player in Yellow zone with a marginal hand facing a strong opponent. M tells you the framework; it doesn't relieve you of the judgment call.

ICM modifies everything at the bubble and final table. M-based strategy is chip-EV-maximising. Near a significant pay jump, the correct strategy tightens up even further than M recommends, because losing chips is disproportionately costly in ICM terms. The ICM deal calculator and the risk of ruin calculator together give you the full picture of how stack depth and prize equity interact.