Moon Phase Calculator
Enter a date and get the moon phase, illumination and moon age from a standard astronomical formula.
Runs in your browser. Nothing is uploaded — your input is processed on this device and discarded when you close the tab.
Moon Phase Calculator
How to use this tool
- Enter your values in the fields above.
- Press Generate to see the result.
- Use Load sample to try the worked example, Copy result to copy it, or Clear to start again.
Worked example
2000-01-21 gives a Full Moon with illumination close to 100%, since it falls about 15 days after the 2000-01-06 new moon.
What this tool does not do / Limits
This is an approximate astronomical calculation from a standard formula. Real new and full moons can differ by hours, and it does not account for your location or local moonrise times.
Frequently asked questions
How accurate is the result?
It is approximate. The formula gives phase and illumination within hours of published times, not to the minute.
Does location matter?
The phase itself is global, but moonrise and moonset times depend on where you are, and this tool does not calculate those.
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