Moon Phase Calculator
See the Moon phase for any date (its name, illuminated percentage and age in days) plus the dates of the next new moon, first quarter, full moon and last quarter. Calculates in your browser.
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How it works
The Moon's phase is found from the angle between the Sun and the Moon as seen from Earth, giving the fraction of the disk that's lit and where in the roughly 29.5-day cycle the Moon is. Age counts the days since the last new moon.
A waxing Moon is growing toward full; a waning Moon is shrinking toward new. The four principal phases (new, first quarter, full and last quarter) are the cycle's quarter points.
Phase times are accurate to within a few hours of published almanacs. Everything is calculated locally in your browser.
What this does
A moon phase calculator shows the Moon’s phase for any date (its name, illuminated percentage, and age in days) plus the dates of the next principal phases.
How to use it
- Choose a date.
- Read the phase name and illumination.
- See the Moon’s age in days.
- Check the dates of the next new, quarter, and full moons.
How it works
Illumination is the fraction of the visible disk lit by the Sun, 0% at new moon, 50% at the quarters, 100% at full. The Moon’s age is the days since the last new moon.
lunar cycle ≈ 29.5 days
Understanding your result
Illumination is the lit fraction of the visible disk, from 0 percent at new moon to 100 percent at full, and the age is days since the last new moon. Use the upcoming-phase dates to plan around dark skies for stargazing or a bright full night, remembering the cycle averages 29.5 days so the dates drift through the calendar month to month.
Example
A full moon shows 100% illumination and an age near 14–15 days.
Sources & methodology
Last updated .
Frequently asked questions
What does the illumination percentage mean?
It’s the fraction of the Moon’s visible disk that’s lit by the Sun, 0% at new moon, 50% at the quarters, and 100% at full moon.
What is the Moon’s age?
The number of days since the last new moon. A full lunar cycle averages about 29.5 days, so a full moon falls near day 14–15.
How precise are the phase dates?
The principal-phase times are computed from the Sun–Moon geometry and land within a few hours of published almanacs, close enough for planning, photography or stargazing.
Is my data stored?
No. Everything is calculated locally in your browser.
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