Moon Phase Calculator
Calculate the moon phase for any given date. Learn about the lunar cycle and see the illuminated fraction.
Published by:
isCalculator Editorial Team
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How to use this tool?
How to Use the Moon Phase Calculator
- Select a date using the date picker field (defaults to today).
- Click the "Calculate Moon Phase" button.
- View the results below the button:
- Phase name (e.g., New Moon, First Quarter, Full Moon).
- Illumination percentage (0% = new, 100% = full).
- Age in days since the last new moon (0–29.5).
- Moonrise/Moonset times (shown as "Varies" due to location dependency).
- If no date is selected, an error message will appear.
Note: The calculator uses a simplified astronomical algorithm based on the Julian Day Number. Moonrise and moonset times are not provided—they depend on your geographic location.
Previous Results
| Result | Inputs | Date |
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Frequently Asked Questions
The calculation is based on the mean lunar cycle length and a known new moon reference. It is accurate to within a few hours for most dates between 1900 and 2100.
We use the synodic month of 29.53058867 days, which is the average time between new moons.
Moonrise and moonset times depend on the observer's latitude and longitude. This calculator provides a general phase calculation; for precise times, use a dedicated almanac.