Moon phase calculator — phase, illumination and next full moon for any date

Choose a date and a UTC time to see the Moon's approximate phase, how much of it is lit, its age since the last new moon, and when the next full and new moons are due.

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How to use the moon phase calculator

  1. Choose a Date. It opens on today’s date by the UTC calendar.
  2. Set Time (UTC), which starts at 12:00.
  3. Read the Phase with its emoji, the Illumination percentage and the Moon age in days since new moon.
  4. Check Direction (waxing or waning), and the approximate Next full moon and Next new moon with their UTC times.
  5. Cycle progress runs from 0% at new moon through 50% at full moon.

What it does and when to use it

Use it to plan stargazing on moonless nights, pick a bright evening for a night photo, check the Moon on a birthday, or teach how the phases repeat.

Easter follows a spring full moon, but the Easter date finder uses the church’s fixed calculation rules rather than the real Moon. To count down to the next full moon, enter its date in the days until calculator.

How it works

The tool counts the time since a known new moon (6 January 2000 at 18:14 UTC) and divides it by the mean synodic month, 29.530588853 days. The remainder is the Moon’s age. From that age:

  • Illumination = (1 − cos(2π × age ÷ 29.53)) ÷ 2, so 0% at new moon and 100% at full moon.
  • Phase name comes from splitting the cycle into eight equal parts, from new moon to waning crescent.
  • Next full and new moon are the times when the age reaches half a cycle and a whole cycle.

The real Moon speeds up and slows down along its elliptical orbit, which this mean model ignores, so results can be off by up to about a day. The tool’s tests check four known new and full moons from 2017 to 2025, each within a day.

Worked examples

7 October 2026, 12:00 UTC. Waning crescent, 16.1% lit, Moon age: 25.6 days since new moon. The next new moon is given as about 11 October 2026, 09:14 UTC, and the next full moon as about 26 October 2026, 03:36 UTC.

20 July 1969, 20:17 UTC (the Apollo 11 landing). The phase name is First quarter, but Illumination: 36.7% and the age is 6.1 days, so the Moon was still a growing crescent just under half lit.

Christmas Eve 2026, 00:00 UTC. Full moon, 99.9% lit, with the exact mean full moon about five hours later at 05:04 UTC.

Limits and tips

  • Moonrise, moonset and the Moon’s height in the sky depend on your location and are not calculated.
  • To see which weekday a full moon falls on, paste its date into the day of the week finder.

Frequently asked questions

How accurate is it?
It uses the average length of the lunar cycle, so the phase name and percentage are good for planning, but the times of the next full and new moon can be several hours to about a day away from the true times. For exact times, use a national observatory's published tables.
Why does the time box say UTC?
The phase is the same everywhere at a given moment, so the tool works in Coordinated Universal Time (UTC). Convert your local time first; for example, 20:00 in New York in summer (UTC−4) is 00:00 UTC the next day.
Does my location change the phase?
The phase and percent lit are the same everywhere at the same moment. What changes is how the Moon looks. In the Southern Hemisphere a waxing Moon is lit on the left rather than the right.
The tool says first quarter, but the Moon is not half lit. Why?
The eight phase names each cover an equal slice of the cycle, about 3.7 days. "First quarter" is shown from roughly 5.5 to 9.2 days after new moon, so the lit part can be anywhere from about 30% to 70% under that name. Use the illumination figure for the exact share.

How do we know nothing is uploaded? Test it yourself on the privacy proof page.

Written by the ToolsRift team · Last updated

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