Moon Phase Calculator
Tonight's moon — phase name, illumination percent and age in days — for any date, with the next full and new moon.
Mean-cycle arithmetic (Meeus): accurate to ±half a day, since real lunations vary ±7 hours with orbital eccentricity. Plenty for fishing, photography, hiking and event planning; for eclipse work or precise moonrise, use a full ephemeris. The same moon phase is seen worldwide on the same night — phases aren't latitude-dependent.
Formula
⚠️ Ephemeris approximations (±1–3 min for sun times at mid-latitudes, ±0.5 day moon age) — ideal for planning; for precise almanac work use USNO/IMCCE data.
Tonight's moon — phase name, illumination percent and age in days — for any date, with the next full and new moon.
About Moon Phase Calculator
The moon runs the sky's only clock everyone can read: a 29.53-day cycle from new to full and back, identical for every observer on Earth the same night. This calculator gives the phase, illumination percentage and lunar age for any date — plus the next full and new moons — using mean-cycle arithmetic honest about its ±half-day envelope. Astrophotographers plan AROUND the full moon, anglers and hunters plan ON it; both need this number first.
How to use Moon Phase Calculator
- 1Enter — sensible defaults are pre-filled so you see a worked result immediately.
- 2Read the live results: .
- 3Check the "With your numbers" line to see the formula age = (date − epoch new moon) mod 29.5306 d; illumination = (1 − cos(2π·age/29.5306))/2 substituted step by step.
- 4Adjust inputs (or flip the unit toggle) until the scenario matches yours, then copy or share the result.
Why use Moon Phase Calculator?
- ✓Instant, free and private — every calculation runs in your browser, nothing is uploaded
- ✓Built on the published formula age = (date − epoch new moon) mod 29.5306 d; illumination = (1 − cos(2π·age/29.5306))/2 with sources cited on the page
- ✓Mean-cycle arithmetic (Meeus): accurate to ±half a day, since real lunations vary ±7 hours with orbital eccentricity. Plenty for fishing, photography, hiking and event planning; for eclipse work or precise moonrise, use a full ephemeris. The same moon phase is seen worldwide on the same night — phases aren't latitude-dependent.
- ✓Switch units, tweak any input and watch every result update live
Frequently asked questions
Why does the moon cycle take 29.5 days when it orbits in 27.3?+
Two different finish lines: the moon completes an orbit relative to the stars in 27.32 days (sidereal month), but meanwhile Earth has moved ~27° along its own orbit — the moon needs two extra days to catch up to the same sun-Earth-moon alignment that defines a phase (synodic month, 29.53 days). Most lunar confusion dissolves with this distinction: phases are about the SUN's angle, not position against the stars.
How does moon phase affect stargazing and astrophotography?+
The full moon is a 400× light-pollution event you can't drive away from: it washes the Milky Way and faint nebulae out entirely — deep-sky imaging season is the week around NEW moon, and the standard planning window is moon below 30% illumination or below the horizon during the session. The flip side: lunar photography itself is best AWAY from full (first/last quarter's grazing light raises crater relief; full moon is flat and shadowless), and landscape photographers prize the 20–60% crescent-to-quarter band for moonlit foregrounds that don't nuke the stars.
Is there anything to fishing and hunting by moon phase?+
The defensible core is tides and light: around new and full moon (spring tides — see our tide tool) coastal currents and water movement strengthen, which demonstrably concentrates feeding windows; bright full-moon nights also shift nocturnal feeding and movement patterns (deer activity measurably redistributes). The solunar-table claims beyond that — minor/major feeding periods at moon transit — have weak evidence but enormous tradition. Phase is one honest input among weather, season and pressure; the calculator at least gets that input right.
Why do full moons have names like 'supermoon' and 'blue moon'?+
Calendar folklore meeting orbital mechanics: a 'supermoon' is a full moon near perigee (the moon's elliptical orbit brings it ~14% larger and ~30% brighter than at apogee — noticeable mostly in photos with reference objects); a 'blue moon' is just the second full moon in a calendar month, an artifact of 29.53 not dividing 30/31 (every 2.7 years); harvest/hunter/wolf moons are seasonal names from agricultural almanacs. None change the physics; all change the search traffic — which is honest to admit on a page like this.
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