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August birthdays: how calendar conversion works
August birthdays can come from several calendars. How Hebrew, Chinese, Islamic and Japanese-era dates convert, and what a converted entry must record.
What to take away
- An entry is complete only when it names the calendar its date was recorded in.
- Hebrew and Chinese dates are lunisolar, so the same date lands on a different Gregorian day in most years.
- Islamic dates move about 11 days earlier each Gregorian year and pass through the seasons in roughly 33 years.
- Japanese era names change the year number and leave the day and the month alone.
The calendars a record can be in
A birth certificate, a family record and a fan page can each hold a different kind of date. Unless an entry says otherwise, this site's August birthdays list holds Gregorian dates. The systems below are the ones most likely to sit behind an August birthday.
How it counts
- Gregorian
- Solar year of 365 or 366 days, twelve fixed months
- Hebrew
- Lunisolar, twelve or thirteen months, a leap month in 7 of every 19 years
- Chinese
- Lunisolar, a leap month in about 7 of every 19 years
- Islamic
- Purely lunar, twelve months, a year of 354 or 355 days
- Japanese era
- Gregorian months, year counted from the start of a reign
What happens to an August birthday
- Gregorian
- Falls on the same date every year
- Hebrew
- Moves within about a month of its Gregorian date
- Chinese
- Moves, and jumps later when a leap month falls first
- Islamic
- Moves about 11 days earlier each year
- Japanese era
- Same day and month, a different year number
[figure 1]
Lunisolar vs Lunar vs Gregorian
Lunisolar
- Months align with
- Moon
- Years align with
- Sun (roughly)
- Correction
- 13th month
- Birthday date
- Moves yearly
- Gregorian record
- Two facts
Lunar
- Months align with
- Moon
- Years align with
- Drift
- Correction
- None
- Birthday date
- Walks seasons
- Gregorian record
- Two facts
Gregorian
- Months align with
- Sun
- Years align with
- Sun
- Correction
- Leap day
- Birthday date
- Fixed
- Gregorian record
- One date
A by-day index such as July birthdays by day stores one date and one sort key for each person. That leaves no room for a second calendar field.
Category labels hide the detail that matters. "Lunar" does not say whether the date is corrected to the seasons, and that correction decides whether an August birthday stays in August.
Example: one Chinese date, two Augusts
Qixi, the seventh day of the seventh lunar month, usually falls in August. In 2024 it fell on August 10. In 2025 it fell on August 29.
That is 19 days later, not the 11 days earlier a lunar date normally moves. The Chinese calendar placed a leap sixth month before it in 2025. A lunisolar calendar inserts a thirteenth month in about 7 of every 19 years, which is why a leap can push a date forward rather than back.
Four steps get from a lunar date to a Gregorian one:
One Chinese date, two Augusts
- Find the start of the lunar year in the Gregorian calendar. Chinese New Year falls between January 21 and February 20.
- Count the lunar months from that start, including any leap month, up to the month named on the record.
- Add the day number inside that month, counting from 1.
- Convert the year separately if the record uses an era or an epoch.
So the seventh day of month seven in 2025 sits seven days into a month that began on August 23. The date is August 29.
Year numbers are their own problem
Two records can agree on the day and the month and still disagree on the year. Japanese era names number years from the start of a reign, so one solar year gets written differently depending on the era it falls in.
Showa 60 is 1985, Heisei 1 is 1989, Reiwa 1 is 2019. An era can begin mid-year too, which splits one Gregorian year across two era years.
[figure 2]
Year numbering systems compared
Japanese era
- Start point
- Reign start
- Offset
- Varies
- Era change
- Mid-year
- Copy error
- Wrong era
Religious epoch
- Start point
- Religious epoch
- Offset
- Fixed
- Era change
- No
- Copy error
- Centuries off
Gregorian
- Start point
- Fixed epoch
- Offset
- None
- Era change
- No
- Copy error
- None
Older entries often leave the source calendar unstated, and the historical figures with September birthdays list inherits the gap, because a list can only show what its records show. Epoch counts carry a fixed offset instead. The Hebrew year runs about 3,760 ahead of the Gregorian year number, and the Islamic year about 579 behind.
What an entry should state
The date alone is not the record. Six fields carry the whole thing.
- The date as written, in the script and system of the source.
- The calendar by nameHebrew, Chinese, Islamic, Gregorian, or the era name.
- Whether a lunisolar or lunar date is the original birth or the recurring observance.
- The converted Gregorian date, with the source or method of the conversion.
- Whether the year, the month and the day all came from the same record.
- The trail behind it, such as a birth certificate or a census entry.
Vital records are the usual place to check a disputed date. In the United States that means the vital records office of the state health department where the person was born, which holds the birth certificate; a certified copy is the document a calendar entry can point to.
Reading a converted date
A converted date is a claim about a claim. If the page will not say who converted it, or whether the year was converted too, it has published a guess with a confident face.
Two checks settle most cases. Who did the conversion, and does the year match the day and month in the same system? Is the date a birth or an observance?
Every conversion is someone's work, and the entry should carry the name of whoever did it.
August birthdays on this site
August is a busy month in two of these systems. The Hebrew month of Elul begins in August in most years, and the seventh month of the Chinese calendar usually begins in August too. The musicians with September birthdays list holds the entries that drift later.
For most entries on the August list the Gregorian date is the whole record, fixed to the same day each year. Where an entry came from a Hebrew or Chinese household, the August date is a conversion. The observance may fall in September this year and return to August later. Both dates can be right.
This site's August list holds Gregorian dates like these:
An August birthday and the record behind it
The simplest August entry is a civil one. Barack Obama was born on August 4, 1961, and every field on the record is Gregorian. The birth certificate is held by the Hawaii Department of Health, the office that keeps the state's vital records, so the day and the month stay exactly where they are.
Michael Jackson's date is August 29, 1958, Gregorian as well, and it stays fixed for the same reason.
Neither entry needs a conversion. The work starts when the record behind an August date was written in a Hebrew or a Chinese household, in that household's own calendar, and the date was later moved onto a Gregorian list.
Common questions
Is a converted date less reliable than a native one?
It sits one step further from the record, and each conversion is a place for an error. A conversion that names its method and source is nearly as good as the original.
Should a site list a lunar birthday under this year's Gregorian date?
Only if it says that is what it is doing and updates the entry every year. Fixing an observance to one Gregorian date is wrong in most years.
Do these problems reach living people?
Constantly. Many people observe a birthday in one calendar and hold documents in another, and both dates are correct in their own life. The month-by-month planning calendar for 2027 covers the weekday arithmetic that assumes a single fixed Gregorian date.
Which calendar should an entry use when the source does not say?
Name the one the document itself uses and leave the Gregorian conversion blank rather than guessed.
In this guide
- Famous August Birthdays and How to Tell Namesakes ApartFamous August birthdays with each person's role, and how a role separates namesakes such as the two Armstrongs, both born in August.
- Actors with August birthdays from the ground upAugust birthdays among actors trace back to studio publicity files, not civil records, so each date needs its source named before it is cited.
- Athletes born in August, and how the dates are checkedAthletes born in August, from Usain Bolt to Kobe Bryant, and the records offices, league guides and time zone quirks that verify each birth date.
