The weekend birth gap by year
Average births per actual weekday or weekend day, U.S. SSA 2000–2014
Bars: weekend shortfall against each year's weekday mean, starting at zero; full scale is 100%. Selected years shown; full 15-year table on the page. Holidays retained. The gap did not grow every year.
Weekdays average more births per day
Tuesday was the most common day of the week to be born, and Sunday the least common, by average daily births in the U.S. SSA records from 2000 through 2014.
Weekdays averaged 12,674.6 births per day, compared with 8,040.5 on weekends in the same records. An average weekend day had 36.6% fewer births than an average weekday.
Counting all weekday births would give weekdays an advantage: there are five weekdays and only two weekend days in a normal week. Dividing by the number of actual days lets us compare their daily averages.
| Group | Recorded births | Observed days | Births per day |
|---|---|---|---|
| Monday to Friday | 49,595,640 | 3,913 | 12,674.6 |
| Saturday and Sunday | 12,591,384 | 1,566 | 8,040.5 |
What is the most common day of the week to be born?
Tuesday had the highest average, at 13,122.4 recorded births per Tuesday. Sunday had the lowest, at 7,518.4 per Sunday. Every weekday has a higher average than either Saturday or Sunday in this dataset.
| Day | Recorded births | Observed days | Births per day |
|---|---|---|---|
| Monday | 9,316,001 | 783 | 11,897.8 |
| Tuesday | 10,274,874 | 783 | 13,122.4 |
| Wednesday | 10,109,130 | 783 | 12,910.8 |
| Thursday | 10,045,436 | 782 | 12,845.8 |
| Friday | 9,850,199 | 782 | 12,596.2 |
| Saturday | 6,704,495 | 783 | 8,562.6 |
| Sunday | 5,886,889 | 783 | 7,518.4 |
The period contains 783 occurrences of most days of the week, but 782 Thursdays and Fridays. Each average uses the actual number of times that day occurred.
The period-wide averages hide some variation between individual years.
Did the weekday and weekend gap change from 2000 to 2014?
Yes. An average weekend day had 31.6% fewer births than an average weekday in 2000, compared with 35.5% fewer in 2014. The gap between the first and last year widened by 3.9 percentage points. That is a change in the relative gap, not a change in the overall number of births.
The difference did not grow steadily every year. Its smallest value was 31.6% in 2000; its largest was 38.9% in 2010. The annual table shows how the gap changed between those endpoints.
| Year | Weekday days | Weekend days | Births per weekday | Births per weekend day | Weekday/weekend ratio |
|---|---|---|---|---|---|
| 2000 | 260 | 106 | 12,481.5 | 8,532.1 | 1.463 |
| 2001 | 261 | 104 | 12,429.4 | 8,335.5 | 1.491 |
| 2002 | 261 | 104 | 12,447.8 | 8,177.2 | 1.522 |
| 2003 | 261 | 104 | 12,682.6 | 8,201.0 | 1.546 |
| 2004 | 262 | 104 | 12,757.4 | 8,119.5 | 1.571 |
| 2005 | 260 | 105 | 12,956.1 | 8,032.1 | 1.613 |
| 2006 | 260 | 105 | 13,336.7 | 8,262.9 | 1.614 |
| 2007 | 261 | 104 | 13,460.0 | 8,343.5 | 1.613 |
| 2008 | 262 | 104 | 13,211.4 | 8,167.0 | 1.618 |
| 2009 | 261 | 104 | 12,912.5 | 7,892.5 | 1.636 |
| 2010 | 261 | 104 | 12,496.7 | 7,637.9 | 1.636 |
| 2011 | 260 | 105 | 12,340.3 | 7,604.1 | 1.623 |
| 2012 | 261 | 105 | 12,234.8 | 7,691.3 | 1.591 |
| 2013 | 261 | 104 | 12,144.7 | 7,726.8 | 1.572 |
| 2014 | 261 | 104 | 12,226.1 | 7,880.0 | 1.552 |
Each row divides that year's weekday births by its actual Monday-through-Friday dates and weekend births by its actual Saturdays and Sundays. A leap year, or the weekday on which a year begins, can change those day counts. Using the actual denominators prevents a longer group from looking busier just because it contains more days.
The weekday-to-weekend mean ratio is 1.463 in the first year and 1.552 in the last. A ratio of 1 would mean equal daily averages. Every observed year's ratio is above 1: weekdays lead in all 15 years.
This is a descriptive comparison within one SSA source series. Holidays keep their actual weekday classification, and the result is not adjusted for delivery method, holiday mix or other changes. The changing gap does not identify its cause.
Why are fewer babies born on weekends?
Scheduled cesarean deliveries help explain the pattern. In its report on U.S. births in 2002, NCHS noted a larger weekend drop for cesarean than vaginal births, especially repeat cesareans. The report links that pattern to repeat cesareans being more likely to be scheduled and less likely to occur on weekends. That explanation comes from birth certificates; our SSA counts do not include delivery methods.
The pattern also appears in NCHS tables for U.S. births in 2014. Table I-3 shows lower weekend averages for both vaginal and cesarean deliveries, with a larger percentage drop for cesareans.
Our SSA file contains dates and birth counts, but no information about labor onset, delivery method, or scheduling. It cannot tell us how much of the weekend difference scheduling explains, or why any individual baby was born on a particular day.
How we counted weekdays and weekends
We used all 62,187,024 births across 5,479 dates in the SSA file, from January 1, 2000 through December 31, 2014. Monday through Friday count as weekdays; Saturday and Sunday count as weekends. Holidays retain their actual weekday classification.
Average births per day = births in the group ÷ actual days in the group
For weekdays, that is 49,595,640 ÷ 3,913. For weekends, it is 12,591,384 ÷ 1,566. To calculate how much lower the weekend average is, we subtract the weekend-to-weekday average ratio from one and multiply by 100.
We use one source series throughout. The main birthday checker combines CDC/NCHS 1994 through 1999 with SSA 2000 through 2014, so its coverage and totals are different. These daily averages adjust for the number of days in each group; they do not adjust for the mix of holidays or other factors affecting birth counts.
Sources and related comparisons
The calculations use FiveThirtyEight's SSA daily birth file, shared under CC BY 4.0 as described in the repository. Download the original analysis data for the overall numerical results, and the annual comparison data for the year-by-year totals, day counts, averages and ratios. See the methodology for the source and calculation boundaries.
The findings describe historical U.S. records. They are not a prediction of an individual baby's birth date or a claim about today's worldwide pattern.
You can also compare birth months: August leads by total births, while September leads per day. For a closer look at particular calendar dates, see births around four selected holidays or use the birthday checker.
Individual-date studies match nearby weekdays to avoid comparing a Tuesday with a Sunday. See March 17 for a small consistent difference, June 21 for a comparison that changes direction, or Memorial Day for actual holiday Mondays.
To find the weekday of your own birth date, use the birth-weekday calculator. That personal calendar result is separate from this population comparison.