GEDitCOM II extension | Mick Reed, REED / MAXWELL Family History | Based on the LifeLines program bday_cover by Andrew Deacon (1994)
A light-hearted look at how the birthdays in your file fall across the year: how many people share each day, which months are busiest, the most shared birthdays, and how many of the 366 possible days are covered — compared with what chance alone would give.
It has a practical side too: a run of births in one month can reflect seasonal patterns of marriage and conception, and a day with an unexpectedly large count can point to duplicated people or a date entered by default.
Lifelines Comparison To see the original Lifelines script that was translated here by AI, open the BirthCalendar.gplug extension in GEDitCOM Editor and look in "Text Files" section. Those with more interest in Lifelines scripts can download/install the Lifelines Emulation extensions for GEDitCOM II.
Choose Birthday Calendar Analysis from the Extensions menu. The whole file is used. If a person is selected when you run it, their birthday is outlined on the calendar and the summary says how many others share it.
How many people have a birth date with a day and month, how many days of the year those birthdays cover, how many would be covered if the same number fell at random, and the largest number sharing one day.
Twelve rows of months by 31 days. Each square shows how many people were born on that day. The squares are shaded by number of standard deviations, σ, from the mean for the expected distribution of birth days:
| Shade | Deviation from Mean |
|---|---|
| <-2σ | |
| -2σ to -σ | |
| -σ to 0 | |
| 0 to +σ | |
| +σ to +2σ | |
| >+2σ |
Because the ranges are rounded to integers, it takes more than about 2500 people with birth date and month for those ranges to closely match standard deviation intervals. Click any number to jump to the people born that day. Hover over a number to see the date and number for that day.
Calendar Squares Coloring: The AI translation choose hard-coding of coloring that was only appropriate for about 2500 people. The above coloring scheme was implemented by translating (and revising) Python code from more AI to calculate shade brackets assuming a binomial distibution. It works better for smaller files and scales well for larger files.
Births in each month, as a number, a percentage and a bar.
Up to fifteen days with the most people, largest first.
Month by month, each day with the people born on it and their birth year, all linked to their records.
12 AUG 1850. Year-only and month-and-year dates are left out.BET, BEF, AFT, FROM, TO) are left out.ABT, EST and CAL dates with a day and month are counted at face value.The chance comparison. With n birthdays spread at random over 366 equally likely days, the expected number of different days is 366 × (1 − (365/366)n). Real birthdays are not spread evenly — there are seasonal peaks, and 29 February is four times rarer than other days — so a real file usually covers a few days fewer than chance. A shortfall much larger than that is worth a look.
| Date | Notes |
|---|---|
| 31 OCT 2026 | GENerel conversion of bday_cover, packaged as an extension: calendar heat map, months, most shared days, chance comparison, everyone by birthday, selected person highlighted (created bhy Mick Reed). |
| 4 NOV 2026 | Updated shading of squares to be calculated from expected binomial distibution of number of people born each day. The help was edited to link to Lifelines extensions and to explain the new shading (updated by John Nairn). |