Moon Phase Calculator (Phase and Illumination by Date)
Pick a date to see the Moon’s approximate phase and when the next full moon is.
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Moon Phase Calculator (Phase and Illumination by Date) by TheCalcTools
How the Moon Phase Calculator (Phase and Illumination by Date) works
The Moon goes from new to full and back in an average synodic month of 29.53 days. The calculator counts days since a reference new moon (6 January 2000, 18:14 UTC) and takes the remainder.
Because the real Moon’s orbit is elliptical, actual phase times can differ from this average by up to about a day. Use an almanac for precise times.
The formula
Worked example
Using the default values shown in the calculator:
| Date | 2026-10-17 |
|---|
- On 17 October 2026 the Moon is about 6.1 days old: First quarter, 37% lit.
- Next full moon around 25 October 2026.
Result:
| Phase | First quarter |
|---|---|
| Illuminated (approx.) | 37% |
| Moon age (days since new moon) | 6.1 |
| Next full moon (approx.) | 25 October 2026 |
| Next new moon (approx.) | 9 November 2026 |
Frequently asked questions
When is the next full moon?
The result shows the approximate date; the exact time can differ by up to a day.
Why is the phase the same everywhere on Earth?
The phase depends on the Sun-Earth-Moon geometry, which is the same for everyone at a given moment; only its orientation in the sky changes.
Sources and further reading
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This calculator gives estimates for information only. Check important results independently before you rely on them. See our disclaimer.