Are more babies born on full moon nights?
No difference
So far, no difference usable for planning or preparation has shown up in the statistics.
- Average (whole period)
- 11,435 births/day
- Births on full moon days (±24h)
- 11,501 births/day
- Births on new moon days (±24h)
- 11,463 births/day
- Data
- 2000–2014, US daily births (SSA), 5,209 days after excluding holidays
Act II: If not the moon, what does decide?
Came looking for a difference? Here is a real one.
−37%
About 37% fewer babies are born on weekends than on weekdays — C-sections and induced deliveries are scheduled for weekdays, when hospitals are fully staffed. A difference far larger than any lunar hypothesis, created by medicine prioritizing safety.
What moves birthdays isn't the moon — it's medical planning for safer deliveries.
The "full moon baby boom" folklore
Maternity wards around the world share the same legend: delivery rooms get busy on full moon nights. The story often comes with a tidal explanation involving amniotic fluid, which makes it one of the most persistent moon myths. It has also been tested in medical research dozens of times — and large datasets almost uniformly report no effect. This page's verdict simply re-runs that test automatically, every day.
How this verdict is computed
We use daily US birth counts (derived from Social Security Administration records, published by FiveThirtyEight, 2000–2014). Raw birth counts cannot be compared with moon phase directly, because births carry a huge weekday pattern (see Act II) and seasonality. So we adjust:
- Expected value for each day = the average for the same "weekday × month" combination (e.g., a Tuesday in July is compared with all Tuesdays in July)
- Index = actual ÷ expected (1.00 = normal)
- Holidays, year-end weeks, and Thanksgiving — where scheduled deliveries are most distorted — are excluded
- Each day is classified as a full moon day (±24h around the instant), new moon day, or other, using the moon age at noon US Eastern Time; the mean index of each group is compared with 1.00
See the methodology for the exact criteria.
Notes
- This covers US data. Japanese daily birth statistics are planned next, using the same method
- The vivid memory of "that one crazy full moon shift" is well explained by confirmation bias — busy full moon nights get remembered, quiet ones don't. The data counts every night equally
Sources
- FiveThirtyEight: births dataset (US daily births from SSA records, CC BY 4.0)
- Moon phase instants computed in-house from Jean Meeus, "Astronomical Algorithms" (UTC)
Last updated: June 11, 2026 13:31 UTC (rebuilt daily)