Is my input uploaded anywhere?

No. Everything is computed in your browser via local JavaScript — the date you enter never leaves your device.

The number of days since the previous new moon. New moon is 0 and full moon is about 14.8, completing a cycle every synodic month (~29.53 days). Moon age is widely used in calendars as a measure of the lunar cycle.

What is the illuminated fraction?

The portion of the moon's disk that appears lit from Earth: 0% at new moon, 100% at full moon, and about 50% at first and last quarter.

It's an approximation based on the mean synodic month. Because the moon's real motion is slightly irregular, the times of new/full moon can differ from the true values by up to about half a day. That's fine for phase names and moon age, but consult dedicated ephemeris data if you need exact astronomical times.

Which time zone is used?

The input is interpreted in your device's local time, and the next-phase times are shown in the same local time. Moon phase is a global phenomenon, so only the displayed clock time changes with your time zone.

How are the phase names chosen?

Moon age is split into 8 segments and labeled with the nearest principal phase (new, waxing crescent, first quarter, waxing gibbous, full, waning gibbous, last quarter, waning crescent).

Back to Time

Moon Phase & Moon Age Calculator

Calculate the moon age, phase (new / first quarter / full / last quarter) and illuminated fraction for any date and time, shown as a moon diagram. Also finds the next new, first-quarter, full, and last-quarter moments. A mean synodic-month approximation that runs entirely in your browser.

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How to use

Pick a date and time to compute the moon age, phase (one of 8: new / first quarter / full / last quarter, etc.) and illuminated fraction at that moment, drawn as a moon diagram. It starts at the current time; the Now button resets to the present. Below, you'll see the next new, first-quarter, full, and last-quarter moments after the chosen time. It's a mean synodic-month (~29.53 days) approximation that runs entirely in your browser.

FAQ

Is my input uploaded anywhere?: No. Everything is computed in your browser via local JavaScript — the date you enter never leaves your device.
What is moon age?: The number of days since the previous new moon. New moon is 0 and full moon is about 14.8, completing a cycle every synodic month (~29.53 days). Moon age is widely used in calendars as a measure of the lunar cycle.
What is the illuminated fraction?: The portion of the moon's disk that appears lit from Earth: 0% at new moon, 100% at full moon, and about 50% at first and last quarter.
How accurate is it?: It's an approximation based on the mean synodic month. Because the moon's real motion is slightly irregular, the times of new/full moon can differ from the true values by up to about half a day. That's fine for phase names and moon age, but consult dedicated ephemeris data if you need exact astronomical times.
Which time zone is used?: The input is interpreted in your device's local time, and the next-phase times are shown in the same local time. Moon phase is a global phenomenon, so only the displayed clock time changes with your time zone.
How are the phase names chosen?: Moon age is split into 8 segments and labeled with the nearest principal phase (new, waxing crescent, first quarter, waxing gibbous, full, waning gibbous, last quarter, waning crescent).

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