How accurate is the moon phase?

It is an astronomical approximation based on the average lunar month and is usually correct to within a few hours of the true phase.

What does illumination mean?

Illumination is the percentage of the moon's visible disc that is lit by the sun. A new moon is near zero and a full moon is near one hundred percent.

What is the difference between waxing and waning?

Waxing means the lit portion is growing towards full, while waning means it is shrinking back towards new.

Date & Time Calculators

Moon Phase Calculator

Find the moon phase, illumination and moon age for any calendar date.

Free browser toolRuns in your browserNo sign-up

Select a date

About the Moon Phase Calculator

The Moon Phase Calculator estimates the phase of the moon for any calendar date, from new moon through full moon and back. It shows the phase name, an illumination percentage and the moon's age in days.

The estimate is based on the average length of the lunar month, called the synodic month, measured from a known new moon. It is accurate to within a few hours, which is fine for planning photography, gardening or events.

The calculation is evaluated at UTC noon for the chosen date and runs entirely in the browser. For exact rise and set times, check a local almanac.

Key features

Moon phase name for any date
Illumination percentage
Moon age in days since the new moon
Waxing or waning indicator

How to use

1Select a date.
2Read the phase name and illustration.
3Review the illumination and moon age values.

Examples

Phase on a date

Input: Select any date

Output: Phase name plus illumination percentage

The moon age is measured in days since the most recent new moon.

Frequently asked questions

How accurate is the moon phase?: It is an astronomical approximation based on the average lunar month and is usually correct to within a few hours of the true phase.
What does illumination mean?: Illumination is the percentage of the moon's visible disc that is lit by the sun. A new moon is near zero and a full moon is near one hundred percent.
What is the difference between waxing and waning?: Waxing means the lit portion is growing towards full, while waning means it is shrinking back towards new.

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