Are more babies born on full moon nights?
No difference
So far, this data doesn't show more births on full moon days. We keep looking — including at why the numbers and the experience on the ward might differ.
- 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: What clearly moved the number of births
Here is the difference this data does show clearly.
−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. Medicine's care for safe deliveries shows up plainly in the numbers.
In this data at least, the day of the week moved births far more than the moon did. We're still looking for the moon's part.
The "full moon baby boom" folklore
Maternity wards around the world share the same saying: delivery rooms get busy on full moon nights. It often comes with a tidal explanation involving amniotic fluid, and it's something people who have worked the ward for years say almost with one voice.
Medical research has tested the idea many times, and large datasets haven't yet shown a clear difference. This page keeps up that check every day with public data. Not finding something isn't the same as it not being there — so we keep looking.
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.
What we can't see yet
This result doesn't mean "the moon has nothing to do with it." Here is what the current method can't see:
- Natural labor on its own: C-sections and inductions are scheduled regardless of the moon. Mixed into the total, they would dilute any lunar effect on births that start naturally
- Time of day: the saying is about the full moon night. Our data is daily, so a rise confined to a few night hours wouldn't show
- Place and era: this is the US-wide average for 2000–2014. Individual regions or hospitals, other countries or other decades might look different
What we want to check next
- Add Japan's vital statistics (daily births) and run the same test
- Find data that separates natural births, or breaks births down by hour
Perhaps the feeling passed down on the ward holds something we haven't yet turned into numbers. We'd like to find it in the data one day.
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: October 7, 2026 00:48 UTC (rebuilt daily)