Moon Age Calculator

Moon age is the number of days that have passed since the last New Moon. Astronomers use it to track the lunar cycle, which lasts about 29.53 days. It’s measured from the exact moment of the New Moon.

We use a known New Moon moment (January 6, 2000, 18:14 UTC) as a starting point and add an average synodic month of 29.53059 days. The Moon age for any chosen date is the difference (modulo the lunar month) from that reference. While not astronomically precise to the minute, it’s very accurate for everyday use.

The eight commonly recognized phases are: New Moon 🌑, Waxing Crescent 🌒, First Quarter 🌓, Waxing Gibbous 🌔, Full Moon 🌕, Waning Gibbous 🌖, Third Quarter 🌗, and Waning Crescent 🌘. Each phase corresponds to a specific range of Moon age and illuminated fraction.

It provides an accuracy of ±0.5 days for any date within the 21st century. Real New Moon times can vary by a few hours due to the Moon’s elliptical orbit, but for phase identification and casual planning the result is more than sufficient.

Many traditions link Moon phases to gardening, fishing, and even hair cutting. While scientific support varies, knowing the exact Moon age helps you follow lunar calendars with confidence.

The calculation is performed in UTC to avoid timezone bias. Day-to-day Moon age changes slowly, so the result is reliable regardless of your local time zone – the phase you see in the sky will match.