Moon Phase Calculator
Gives a close idea of the moon’s phase on a date, in the past or the future.
Share sends a link that reopens these numbers. Copy details pastes the full breakdown as a list.
The formula
age = (days since a known new moon) mod 29.530588853 lit share = (1 − cos(2π × age ÷ 29.530588853)) ÷ 2
Counted from the new moon of 6 January 2000 at 18:14 UTC, using the mean synodic month. It is taken at midday UTC on the date.
What to watch out for
The phase names each cover about 3.7 days here. For an exact moment, such as for an eclipse, use a published almanac.
Frequently Asked Questions
How long is a lunar cycle?
On average 29.53 days from new moon to new moon, which is why the phases drift earlier in the calendar month each year.
What was the moon doing on 8 April 2024?
The total solar eclipse of that day came at a new moon, and this method gives an age of 0.4 days from new: “New moon”.