Do home runs rise on full-moon nights?
No difference
These are home-run totals (both teams) for every Major League game. Because the myth is about the full-moon night, we split night games from day games.
Night games
- Average (whole period)
- 1.84 per game
- Full moon days (±24h)
- 1.85 per game
- New moon days (±24h)
- 1.85 per game
- Verdict for full moon days
- No difference
- Data
- 1935–2025, 179,041 HR
Day games
- Average (whole period)
- 1.30 per game
- Full moon days (±24h)
- 1.30 per game
- New moon days (±24h)
- 1.28 per game
- Verdict for full moon days
- No difference
- Data
- 1901–2025, 150,004 HR
Act II: If not the moon, what drives home runs?
Came looking for a difference? Here is a real one.
×5.2
Home runs per game peaked at 2.82 in 2019 and sank to 0.54 in 1944. What drives the long ball isn't the moon; it's the era and the ball — some years it carries, some years it doesn't.
The wildest day for home runs was July 2, 2002 — 62 of them across 15 games. The trigger wasn't a full moon; it was that day's hitting and ballparks.
On a night when the balls keep flying out, look at that year's ball, the size of the parks, and the summer heat before you blame the moon.
The folklore that the ball flies on full-moon nights
Ballparks have long carried the saying that home runs come out under a full moon. A full moon stirs the batter up; a bright night makes hitters swing for the fences — it's the same family of folklore as the myths about crime and accidents. And the heart of the moon myth is always the full-moon night. If that were true, the effect should show up in night games, when the moon is actually in the sky, not in day games. So do home runs really rise on full-moon days? This page checks it every day across every Major League game.
How this verdict is calculated
- The data is home-run totals (both teams) for every Major League Baseball (MLB) game. We split games into night games and day games — because the myth is about the night, that's where any effect should appear
- Home runs per game vary enormously by era (almost none in the dead-ball years, soaring in the recent "juiced ball" seasons). So we use the home runs per game for the same year and month as the expected baseline, and compare the observed-to-expected index
- Using the moon's age at noon (US Eastern) on each game day, we mark full-moon days (within ±24h of the exact moment) and new-moon days, and compare each group's average index against normal (1.00)
See the methodology for the full criteria.
Reading the data
- Home-run totals depend heavily on the size of the ballparks, that year's ball, the temperature, and altitude (the ball carries in thin air). This page levels those out by comparing within the same year and month, and looks only at the single question of the full moon
- This isn't a denial of the clubhouse feeling that "the ball flies on full-moon nights." All this page asks is whether home runs per game visibly rise on the calendar's full-moon days
Data sources
- Retrosheet — Game Logs (date, day/night, and home runs for every game)
- The information used here was obtained free of charge from and is copyrighted by Retrosheet.
- The moon's age and the exact syzygy moments are computed in-house using the algorithms in Jean Meeus, "Astronomical Algorithms" (UTC basis)
Last updated: June 13, 2026 13:25 UTC (rebuilt daily)