Moon phase calculator

Pick a date. The calculator ages the Moon from the reference new moon on 6 January 2000, 18:14 UTC, and names the phase. 25 March 2024 is full moon, about 100%, age 14.6 days. 15 May 1990 is waning gibbous, 72.9%. Simplified calendar astronomy, not a reading.

A UTC synodic sketch, not a horoscope. Sign: zodiac sign. Year: Chinese zodiac. Article: Moon phase.

Input

Result

Pick a date to see the moon phase.

How it works

Phase describes how much of the disc looks lit from new moon to new moon. The mean period is about 29.53058867 days. Age = (UTC date − the 6 January 2000, 18:14 UTC new moon) mod that period. Illumination ≈ 0.5 · (1 − cos(2π · age / period)). Full moon near 100%, new moon near 0%.

25 March 2024: full moon, 100%, age 14.6 days. 6 January 2000: new moon, 0.7%, age 28.8 days, next to the reference. 15 May 1990: waning gibbous, 72.9%, age 19.9 days. 24 January 2023: waxing crescent, 4.6%, age 2.0 days. 1 January 2023: first quarter, 62.3%. 13 January 2023: last quarter, 66.6%.

Names come from age bands: new moon, waxing crescent, first quarter, waxing gibbous, full moon, waning gibbous, last quarter, waning crescent. This is not a scientific weather forecast and not “day energy.” Tight ephemerides use local hour and small orbital wiggles. Here we stay on UTC and a mean period on purpose.

Do not mix phase with the Sun sign or the Chinese year. The Moon sign next door is another layer: ecliptic longitude, not lighting.

One field: date as YYYY-MM-DD. Click Calculate. The same civil date repeats the same result in this model.

Treat the calculator as a synodic-cycle exercise. Do not read the phase as a fortune, a horoscope, or a day’s instructions.

Formula

age = (dateUTC − new_moon_ref) mod 29.53058867 (days).

illumination ≈ 0.5 · (1 − cos(2π · age / 29.53058867)), then map age to a phase name.

How to use

  1. Pick the date in the date field, YYYY-MM-DD. We use the UTC calendar day.
  2. Click Calculate. The result is the phase name, illumination percent, and age in days.
  3. Check 25 March 2024: full moon, about 100%, age 14.6 days.
  4. Near the reference, open 6 January 2000: new moon, 0.7%, age 28.8 days.
  5. Compare the Sun sign or the Moon sign for the same date. Those are different questions.

Moon age from the 2000 new moon

25 March 2024 is a full moon, about 100% and age 14.6 days. A UTC model from 6 January 2000, not a horoscope.

full
The phase near age 14.6 days. 25 March 2024 is close to 100%. Simplified calendar astronomy.
Moon
Age from the 6 January 2000, 18:14 UTC new moon. 15 May 1990 is a waning gibbous, 72.9%. Not a reading.

Suggested uses

  • Quickly check whether a date sits near new or full moon.
  • Learn the synodic cycle and phase names with examples.
  • Compare a few dates by disc illumination.
  • Draft an educational note about the lunar cycle.
  • Pair the phase with biorhythms or a birth sign (entertainment).
  • Verify a hand calculation of age from the reference new moon.

Examples

Example 1

  • Date: 2000-01-06

New Moon · 0.7% · age 28.8 d

Moon phase on 6 January 2000? New moon, 0.7%.

Example 2

  • Date: 2024-03-25

Full Moon · 100% · age 14.6 d

Moon phase on 25 March 2024? Full moon, about 100%.

Example 3

  • Date: 2023-01-24

Waxing Crescent · 4.6% · age 2.0 d

Moon phase on 24 January 2023? Waxing crescent.

Example 4

  • Date: 2023-01-01

First Quarter · 62.3% · age 8.6 d

About a quarter of the way from new to full.

Example 5

  • Date: 1990-05-15

Waning Gibbous · 72.9% · age 19.9 d

After full moon: waning gibbous.

Example 6

  • Date: 2023-01-13

Last Quarter · 66.6% · age 20.6 d

Heading back toward new moon: last quarter.

Related calculators

Zodiac sign

Pick a birth date.

Use calculator →

Chinese zodiac

Chinese zodiac: a birth year.

Use calculator →

Biorhythms

From birth date to a chosen day you compute three sine waves: 23-day physical, 28-day emotional, 33-day intellectual.

Use calculator →

Birthstone

Birthstone calculator: the birth month as a number from 1 to 12.

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All esoteric calculators

Frequently asked questions

What phase is 25 March 2024?

Full moon, about 100%, age 14.6 days. Mid-cycle in this model.

What about 6 January 2000 and 15 May 1990?

2000-01-06 is new moon, 0.7%, age 28.8 days. 1990-05-15 is waning gibbous, 72.9%, age 19.9 days.

Is this a horoscope?

No. It is simplified calendar astronomy. It does not predict weather or a day’s fate.

Where does lunar age come from?

From the day difference versus the 6 January 2000, 18:14 UTC new moon, modulo 29.53058867 days.

Is the result as tight as an ephemeris?

It is a UTC sketch. Professional tables can be tighter on hour and location.

What does illumination percent mean?

The share of the disc that looks lit in this formula. Full moon ≈ 100%, new moon ≈ 0%.

How many phase names are there?

Eight: new moon, waxing crescent, first quarter, waxing gibbous, full moon, waning gibbous, last quarter, waning crescent.

What about 24 January 2023?

Waxing crescent, 4.6%, age 2.0 days, soon after new moon.

How does phase differ from Moon sign?

Phase is lighting. The Moon-sign card next door is mean ecliptic longitude.

Is a blank date the year-2000 new moon?

No. Without a date there is no age. Pick a day on the calendar.

Knowledge sources

The phase in this calculator follows the Moon cycle. NASA describes the same cycle; a horoscope is not in the formula.

Page updated in 2026.