🌕 Moon Phase & Lunar Calendar Tracker
A moon phase tracker showing the current phase, illumination percentage, lunar age, and the exact countdown to the next Full Moon and New Moon.
What Moon Phase & Lunar Calendar Tracker Does
The moon takes about 29.53 days to go from new moon to new moon — the synodic month. That average is where most phase calculators stop, and it is not good enough: the moon's orbit is elliptical, so it does not travel at a constant rate, and consecutive synodic months in late 2026 run from 29 days 7 hours to 29 days 15 hours. Nearly eight hours of variation between one month and the next.
Stepping forward by the mean from a known new moon accumulates that error. Checked against published lunar tables, it lands up to 21 hours out — and 21 hours is 3% of a cycle, which near a quarter moon is about nine percentage points of illumination. So the error is not confined to the "next full moon" date; it is in the headline number.
This uses the periodic corrections from Meeus's Astronomical Algorithms instead, which express the true instant as the mean plus a series of terms for the moon's and the sun's positions. Checked against published times for thirteen consecutive phase events, every one agreed to under three minutes.
Illumination follows from the phase as a cosine, not a straight line. A calculator that interpolates linearly between the named phases is out by up to 10.5 percentage points in the middle of the gibbous phases — the disc fills much faster around the quarters than a clock suggests.
How to Use Moon Phase & Lunar Calendar Tracker
- Select any date to view historical or future lunar positioning
- Review the current moon phase icon, illumination percentage, and lunar age
- Check the countdown days until the next Full Moon and New Moon
Formula Used by Moon Phase & Lunar Calendar Tracker
True phase instants, and illumination
JDE = mean phase + Σ periodic corrections; illumination = (1 − cos(2π · phase)) ÷ 2
- mean phase
- 2451550.09766 + 29.530588861·k, where k counts lunations from January 2000
- corrections
- terms in the moon's mean anomaly, the sun's mean anomaly and the argument of latitude — the largest is 0.407 days
- phase
- 0 at new moon, 0.25 first quarter, 0.5 full, 0.75 last quarter
Worked example
The full moon of 26 September 2026.
- Mean phase for that lunation, then the corrections applied
- Result: 26 September 16:50 UTC against a published 16:49
- Illumination at that instant: (1 − cos π) ÷ 2 = 1
Result: 100.0% illuminated, one minute from the published time. The mean-only method would have placed the preceding new moon 20.7 hours late.
The synodic month is not constant
Consecutive lunations in 2026. The mean is 29d 12h 44m; none of these equals it.
| Lunation | Length |
|---|---|
| July–August | 29d 07h 53m |
| August–September | 29d 09h 50m |
| September–October | 29d 12h 23m |
| October–November | 29d 15h 12m |
The phases, and what illumination each carries
The quarter points are instants, not periods — the named phases between them are the intervals.
| Phase | Cycle position | Illuminated |
|---|---|---|
| New moon | 0 | 0% |
| Waxing crescent | 0 – 0.25 | 0 – 50% |
| First quarter | 0.25 | 50% |
| Waxing gibbous | 0.25 – 0.5 | 50 – 100% |
| Full moon | 0.5 | 100% |
| Waning gibbous | 0.5 – 0.75 | 100 – 50% |
| Last quarter | 0.75 | 50% |
| Waning crescent | 0.75 – 1 | 50 – 0% |
How to Read Your Result
A "quarter" moon looks half lit
First and last quarter are named for position in the cycle — one quarter and three quarters of the way round — not for how much you can see. At both, exactly half the visible disc is lit. The names describe the orbit; the appearance is a separate question.
Which side is lit depends on your hemisphere
A waxing crescent is lit on the right from the northern hemisphere and on the left from the southern. Near the equator it can appear lit from below, like a bowl. The symbols on this page are drawn for the northern hemisphere, so southern readers should mirror them.
Full moon is an instant, not a night
The moon is only exactly full for a moment. It looks full to the eye for roughly three nights either side, because the difference between 98% and 100% illumination is not something people can see. That is why almanac dates and what you observe rarely feel like they disagree.
The dates here are UTC
A full moon at 00:30 UTC falls on the previous evening across the Americas, which is why moon phase dates differ between calendars printed in different countries. Convert to your own timezone before planning around one.
Limitations & Accuracy Notes
- Phase instants use the principal periodic terms, giving agreement within a few minutes rather than seconds. Full precision needs the complete series.
- Illumination is of the disc as seen from the center of the Earth. Your position on the surface shifts it very slightly.
- Moonrise and moonset are not calculated — they depend on your latitude and longitude and are a separate problem.
- Supermoons, eclipses and lunar distance are outside the scope of this.
- Times are UTC throughout.
Frequently Asked Questions
What are the 8 primary moon phases in order?
How long is a complete lunar cycle (synodic month)?
How long is a lunar cycle?
Why does the Moon look different from the southern hemisphere?
What is a supermoon?
Why can I see the Moon during the day?
What is earthshine?
Is the phase calculated or looked up?
References & Further Reading
- Jean Meeus, Astronomical Algorithms — Chapter 49, "Phases of the Moon" — the periodic corrections implemented here