A life measured in moons
Long before calendars were printed, people kept time by the Moon. A “month” is literally a moon-th, and many cultures still set festivals by the lunar cycle. Counting the full moons you have lived through is a lovely way to see a life in a much older unit. Most adults have seen more than 400 of them, though clouds and city lights mean you probably noticed only a fraction.
The chart above has one row for each year of your life, starting with the year you were born. Each glowing dot is a full moon, placed along the row by its date, so you can see the moons drift a little earlier each year. Blue dots are blue moons, the second full moon in one calendar month.
How we calculate it
The Moon goes from new to full and back in an average of 29.530589 days. We start from a known new moon on 6 January 2000 and step forward or back in whole cycles. Half a cycle after each new moon is a full moon. Counting those between your birth date and today gives your total. Because the real cycle speeds up and slows down slightly, individual dates can be off by up to about half a day, which is why we say “about”. The phase picture uses the same method for your birth date.
| Month | Traditional name | Month | Traditional name |
|---|---|---|---|
| January | Wolf Moon | July | Buck Moon |
| February | Snow Moon | August | Sturgeon Moon |
| March | Worm Moon | September | Corn or Harvest Moon |
| April | Pink Moon | October | Hunter’s Moon |
| May | Flower Moon | November | Beaver Moon |
| June | Strawberry Moon | December | Cold Moon |
Worked example. Someone born on 12 April 1990 had lived 13,350 days by 30 October 2026. Dividing by 29.53 gives 452.1, so they have seen about 452 full moons. The Moon was a waning gibbous, about two days past full, on the day they were born.
Once in a blue moon
Because 12 lunar cycles take only about 354 days, the full moons slip roughly 11 days earlier each calendar year. Every two or three years that slippage squeezes two full moons into one month, and the second is called a blue moon. Over a long life you will see a few dozen of them, which makes “once in a blue moon” rarer than everyday life but far more common than the phrase suggests.
Questions people ask
How often is there a full moon?
Every 29.53 days on average, the length of the Moon’s cycle of phases (the synodic month). That gives 12 full moons in most years and 13 in about one year in three.
What is a blue moon?
In popular use, the second full moon in a single calendar month. It happens roughly every two and a half to three years. An older definition is the third full moon in a season that has four.
Why might a date be off by a day?
We use the average length of the lunar cycle, which can put a full moon up to about half a day early or late, and the exact moment of full moon falls on different calendar dates in different time zones.
What phase was the Moon when I was born?
The picture at the top shows it. It is worked out from how far through its 29.53-day cycle the Moon was on your birth date.
Sources. Mean synodic month 29.530589 days and reference new moon of 6 January 2000 (Jean Meeus, Astronomical Algorithms); traditional moon names as popularised by the Old Farmer’s Almanac. Calculations run in your browser; nothing you enter is sent anywhere.