Moon Phase Calculator — Find Moon Phase for Any Date
Calculate the moon phase for any date. Shows the phase name, illumination percentage, and next full moon date. See also our Zodiac Sign Calculator and Date Calculator.
How to Find the Moon Phase
- Enter any date (past or future).
- Click Calculate to see the moon phase.
- View the phase name, illumination percentage, and cycle day.
- The lunar cycle is approximately 29.53 days.
- The next full moon date is also calculated.
Formula
Julian Day Number = 365.25 x (Y+4716) + 30.6001 x (M+1) + D - 1524.5
Days Since Known New Moon = JD - 2451549.5
Lunations = Days / 29.53058770576
Phase = fractional part x 8 (maps to 8 phases)
Example
Date: January 13, 2025
Julian Day calculated, days since reference new moon found
Fractional lunation determines phase position
Result: Full Moon, ~100% illumination
Moon Phases Reference
| Phase | Illumination | Cycle Day |
|---|---|---|
| New Moon | 0% | 0 |
| Waxing Crescent | 1-49% | 1-7 |
| First Quarter | 50% | 7.4 |
| Waxing Gibbous | 51-99% | 7-15 |
| Full Moon | 100% | 14.8 |
| Waning Gibbous | 99-51% | 15-22 |
| Last Quarter | 50% | 22.1 |
| Waning Crescent | 49-1% | 22-29 |
Frequently Asked Questions
How long is a lunar cycle?
A synodic month (new moon to new moon) is approximately 29.53 days. This is different from a sidereal month (27.32 days) which measures the moon's orbit relative to stars.
How accurate is this calculator?
This uses a simplified algorithm accurate to within about 1 day. For precise astronomical data, consult NASA or the US Naval Observatory.
Does the moon affect tides?
Yes. The moon's gravitational pull causes ocean tides. Spring tides (highest) occur during full and new moons; neap tides (lowest) during quarter moons.
What is a supermoon?
A supermoon occurs when a full moon coincides with the moon's closest approach to Earth (perigee), making it appear about 14% larger and 30% brighter.
Can I see the moon during the day?
Yes. The moon is visible during daytime for about half of each month, particularly during first and last quarter phases when it is above the horizon during daylight hours.