The Moon goes through its cycle of phases every synodic month of about 29.53 days. This calculator uses the mean cycle, so times can be off by up to about half a day from the true astronomical phase, which varies because of the Moon’s elliptical orbit.
How to use the Moon Phase Calculator
- Date
- Time (UTC)
Results update as you type, and every field accepts the units shown in its menu.
How it works
Pick a date and time (in UTC – the phase is the same worldwide, only the local date may differ).
Tips
- Check whether the end date should be included – event durations usually include it, elapsed time does not.
- Months have 28–31 days, so “one month” is counted by calendar date, not as 30 days.
- Use 24-hour time or set AM/PM carefully when entering clock times.
- Time zones and daylight-saving changes are not applied unless the calculator says so.
Common mistakes to avoid
- Counting a 30-day month when a calendar month is meant (or the reverse).
- Forgetting leap years when counting days across February.
- Mixing decimal hours (7.5 h) with clock time (7:30).
Inputs explained
| Field | What to enter |
|---|---|
| Date | A date |
| Time (UTC) | A clock time (hours and minutes) |
What each result means
- Moon age = mod([Date] + [Time (UTC)]÷24 – 10962.7597, 29.530588853)
- Illuminated = (1 – cos(2×pi×[Moon age]÷29.530588853))÷2×100
- Next full moon = [Date] + [Time (UTC)]÷24 + mod(14.7652944265 – [Moon age], 29.530588853)
- Next new moon = [Date] + [Time (UTC)]÷24 + 29.530588853 – [Moon age]
Formula
Moon age = (date − known new moon of 6 Jan 2000, 18:14 UTC) mod 29.5306 daysIllumination = (1 − cos(2π × age ÷ 29.5306)) ÷ 2Worked example
Inputs — Date: 2026-10-25; Time (UTC): 12:00.
Results — Moon age = 14.1 days; Phase = Full moon 🌕; Illuminated = 100 %; Next full moon = Mon, October 26, 2026; Next new moon = Mon, November 9, 2026.
Frequently asked questions
What is the moon phase today?
See the result – it uses today's date at noon UTC by default.
How long is a lunar cycle?
About 29.53 days from new moon to new moon.
What is a waxing moon?
One that is growing – between new moon and full moon.
What formula does the Moon Phase Calculator use?
Moon age = (date − known new moon of 6 Jan 2000, 18:14 UTC) mod 29.5306 days.