Example 1
- Date: 2000-01-06
New Moon · 0.7% · age 28.8 d
Near the reference new moon; illumination almost zero.
Moon phase calculator
From the date you approximate the phase in the synodic cycle, about 29.53 days from new moon to new moon. That is disc illumination, not a moon sign.
Here you compute the disc phase in the synodic cycle. This tool is for entertainment and learning, not fortune-telling or life advice. It does not replace personal, medical or financial decisions. Also try the zodiac sign, Chinese zodiac and biorhythms.
Result
Pick a date to see the moon phase.
How it works
The moon phase describes how much of the disc looks lit in the synodic cycle (new moon to new moon). The mean period is about 29.53058867 days.
The model starts from a known reference new moon (6 January 2000, 18:14 UTC) and takes lunar age as the remainder of day difference divided by the synodic period.
Illumination is approximated by 0.5 · (1 − cos(2π · age / period)). Full moon is ~100%, new moon ~0%.
Phase names come from age bands: new moon, waxing crescent, first quarter, waxing gibbous, full moon, waning gibbous, last quarter, waning crescent.
Example: 2024-03-25 → full moon (~100%). 2000-01-06 → near new moon. 1990-05-15 → waning gibbous.
This is not a horoscope or “day energy” reading. It is simplified calendar astronomy. Do not confuse it with the Sun sign or the Chinese year animal.
Precise ephemerides include local time, longitude and small orbital wobbles. Here we keep a clear UTC approximation on purpose.
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 the calculator
- Choose a date in YYYY-MM-DD format.
- Click Calculate or wait for the live result.
- Read the phase name, synodic age and illumination.
- The metric/US switch relabels units and does not convert a number you already typed.
- For fun, pair the phase with biorhythms on the same date.
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 2
- Date: 2024-03-25
Full Moon · 100% · age 14.6 d
Mid-cycle: full moon, peak illumination.
Example 3
- Date: 2023-01-24
Waxing Crescent · 4.6% · age 2.0 d
Soon after new moon: a thin 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.
Example 7
- Date: 12
Result on the card after fill
What is moon phase calculator of 12?
Example 8
- Date: 24
Result on the card after fill
What is moon phase calculator of 24?
Related calculators
Frequently asked questions
What is a moon phase?
The look of the lit portion of the disc in the cycle from new moon to new moon. It does not predict weather or “day fate”.
Where does synodic age come from?
From the day difference versus a known reference new moon, taken modulo the mean ~29.53-day period.
Is the result astronomically exact?
It is a deliberate UTC approximation. Professional ephemerides can be tighter on hour and location.
What does illumination percent mean?
The share of the disc that looks lit in the simplified model. Full moon ~100%, new moon ~0%.
How many phase names are there?
Eight popular labels: new, two crescents, two quarters, two gibbous stages and full.
Is this fortune-telling or a ritual guide?
No. The calculator is entertainment and education. It does not replace specialist advice or life decisions.
Does the clock time matter?
The model uses the calendar date in UTC. Local clock time can shift the phase near a day boundary.
How is Moon phase calculator different from Zodiac sign?
A Sun sign labels a birth date range. Moon phase describes the lunar cycle for a chosen date.
What phase is 2000-01-06 versus 2024-03-25?
6 January 2000: new moon, about 0.7% and age 28.8 d. 25 March 2024: full moon, 100% and age 14.6 d. UTC from the date, not the hour.
Does a blank date take today full moon?
No. It needs an ISO date. 2024-03-25 is in the full-moon example. A blank field does not insert 100%.