Perfect-Season Odds Calculator
A 162-0 season only happens if you win every game — Opening Day through Game 162, no off day for a loss. Set how good a favorite your team is each game, and this tool shows the odds of running the entire table, plus the math, so you can see exactly why baseball's perfect record has never been kept.
From the scorebook: no real team is a heavy favorite every game. The best regular seasons ever — the 2001 Mariners (116-46) and 1906 Cubs (116-36) — won only about 62–76% of individual games. A .650 club (65% here) is already a ~105-win, historically elite season.
The math, in one line
If your team wins each game with probability p, and you treat the games as independent, the chance of winning all 162 is simply:
P(perfect) = p162
That exponent is the whole story. Because you multiply a number below 1 by itself 162 times, the result collapses past every intuition. To have even a coin-flip (50%) shot at a perfect 162-0 season, you would need to be a 99.6% favorite every single game — a win rate that would translate to roughly a 161-1 true-talent pace. No pitching staff in history has come within a country mile of it.
Sensitivity table
How the perfect-season odds change with your per-game win rate, over a full 162-game schedule:
| Win probability per game | Chance of 162-0 | Odds |
|---|---|---|
| 55% | 8.7e-41% | 1 in 1.2 × 10^42 |
| 60% | 1.1e-34% | 1 in 8.7 × 10^35 |
| 65% | 4.9e-29% | 1 in 2.0 × 10^30 |
| 70% | 8.1e-24% | 1 in 1.2 × 10^25 |
| 75% | 5.8e-19% | 1 in 1.7 × 10^20 |
| 80% | 2.0e-14% | 1 in 5.0 × 10^15 |
| 90% | 3.9e-6% | 1 in 2.6 × 10^7 |
| 95% | 0.025% | 1 in 4,062 |
| 99% | 19.6% | 1 in 5.1 |
Read that column top to bottom and the point makes itself: across every win rate a real baseball team could plausibly post, the chance of 162-0 rounds to zero. Even the fantasy 95% club — better than any team that has ever existed — lands at odds a lottery player would laugh at. That isn't a bug in the model. It is the model.
Why the real odds are even longer
This calculator assumes a constant win probability and independent games. Real baseball breaks both assumptions, and nearly every way it breaks them makes perfection harder: an ace can only start every fifth day, so most games go to lesser arms; a bullpen worn down by a daily schedule leaks late runs in August; a single injury or a well-timed cold streak swings a series. The in-game engine on 162-0 models those forces directly — read the full methodology to see how, dig into the arithmetic in why 162-0 is effectively impossible, then spin an era and take your own nine for a run.