Learn · 2019–2025, 224 team-seasons
How much of an NFL season is luck?
About 39% of the spread in NFL regular-season records is luck. Two different measurements agree: 40% from how far records spread compared with a league of coin flips, and 37% from replaying every game with the way both teams actually played.
The coin-flip test
If every NFL game were a coin flip, records would still spread out: over 17 games, chance alone moves a team a couple of wins either side of .500. Compare that spread with the one real records show, and the ratio is the share of the variation that luck could account for. It’s the method Michael Mauboussin popularised in The Success Equation. On the 2019–2025 regular seasons it gives 40%.
The replay test
We can also measure luck game by game. Replay each game 4,000 times with the way both teams actually played and count how often each team wins; add that up over a season and compare it with the real record. The gap between them is luck, and it accounts for 37% of the variation in wins. A typical team’s record is off by about 1.9 wins from what its play was worth, in a league where records vary by about 3.2 wins.
Only the bounces
The narrowest version re-rolls only the chance events (kicks, fumble bounces, drops, conversions, judgment calls) and keeps everything else. Those alone account for 24%. The rest of the luck is in the sequencing: which drives the big plays land on, and when.
Other sports
By the coin-flip test, basketball is the most skill-driven of the major leagues and hockey the most luck-driven, with football in between (SIAM News has an overview). Football’s short season does a lot of the work: 17 games leave more room for chance than 82. When we add other sports, this page will compare them with the same two tests.
Who got lucky in 2026 · What every team’s play was worth · Methodology