What are the most common birthdays?

The leader depends on the dataset

September 12 has 191,024 births in this fifteen-year SSA sample. That is about one in 326 of the 62,187,024 records, and an average of 12,735 births each time the date occurred. It takes rank #1. September 19 follows with 190,435 births, while September 20 has 188,123. The table shows the first thirty dates in descending count order.

Those exact figures come from the same data used by the calculator. We have not copied a birthday ranking from another site or selected the date that appears most often in headlines. If you have seen September 9 named first, compare September 9 and September 12 in the full month table. Different sources and date ranges can produce different leaders without either calculation being an arithmetic error.

Common dates are not evenly spaced

Several leading dates fall close together in September. The August table lets you examine the preceding month, and October continues the comparison afterward. A seasonal pattern in recorded births is not enough to determine when a particular person was conceived, predict a due date or explain a delivery decision. This tool answers a narrower question: how frequent was this calendar birthday in the sample?

The “rarer than” column can be close to zero for dates near the top. That does not mean the birthday is impossible or uninteresting. It means very few other calendar dates have a higher count. The percentage compares dates; the “1 in” number compares birth records. Keeping those two units separate makes the result easier to interpret.

Compare your birthday with the leading dates

Choose your month and day above to get a personal result card. If your date is outside the top thirty, its row still appears in the relevant month table. The opposite end of the distribution is on the rarest birthdays page, where leap day and fixed annual holidays show why equal-probability assumptions miss real differences.

These are U.S. birth records from 2000–2014, not worldwide data or a count of living people. The methodology documents the source, treatment of February 29, ranking formula and rounding used in every display and export.