How accurate is the calculation?

Very accurate. The lunar cycle is predictable, averaging 29.5306 days, and modern formulas account for orbital eccentricity and perturbations. Accuracy is typically within hours for any date in the past or near future. Rare phenomena like eclipses require specialized calculations.

Why do moon phases happen?

The Moon orbits Earth and the Sun illuminates the Moon from one direction. As the Moon moves around its orbit, we see different fractions of the illuminated side. The same lit half always faces the Sun; we just see varying fractions of it. The cycle goes from new (Sun behind the Moon, dark side facing us) to full (Sun behind us, lit side facing us).

What's a 'supermoon'?

A supermoon is a full moon that occurs when the Moon is at perigee, the closest point in its elliptical orbit. It appears about 14 percent larger and 30 percent brighter than a micromoon (an apogee full moon). The visual effect is modest, and the term is mostly used in awareness and marketing. There are several per year, and the tool may identify these dates.

How do moon phases affect tides?

Significantly. New and full moons produce spring tides, with the largest difference between high and low. First and last quarters produce neap tides, with smaller differences. The Sun's gravity adds to or subtracts from the Moon's. This matters for fishing, boating, and beach activities.

There are two definitions. The first is the second full moon in a calendar month, which is rare — roughly once every two or three years. The second is the third full moon in a season that has four (the older definition). The phrase 'once in a blue moon' refers to that rarity. The tool may identify these dates. The color does not actually change.

Does the moon look different from Southern hemisphere?

Yes — the phase appears reversed. A waxing crescent in the Northern Hemisphere (with the curve on the right) looks like a waning crescent in the Southern Hemisphere (with the curve on the left). It is the same physical phase, just a different orientation due to the viewing angle. Travelers to the other hemisphere often find this confusing.

Is the data sent anywhere?

No. Moon phase calculation is pure math — lunar cycle modular arithmetic — running entirely in your browser. Your dates never leave your device.

Moon Phase Calculator

Calculate the moon phase for any date with visual representation. See full moon, new moon, and lunar cycle data. Free moon phase tool.

Date & Time Calculators

Instant results

Select Date

Date

Waning Crescent

Monday, May 11, 2026

27.9%

Illumination

24.3

Days into Cycle

Days to Full Moon

Days to New Moon

Upcoming Phases

Lunar Cycle Progress

New MoonFirst QuarterFull MoonThird QuarterNew Moon

About Moon Phase Calculator

Calculate the moon phase for any date using the synodic period algorithm (29.53-day cycle). Shows phase name, illumination percentage, days until next full and new moons, and a visual representation. Based on astronomical calculations from a known new moon reference date.

How to Use Moon Phase Calculator

Pick a date

Use today's date by default, or specify any past or future date. The tool calculates the phase for that day.

View phase details

The display covers the phase name, illumination percentage, days since the new moon, and days to the next full or new moon, alongside a visual moon icon.

Browse calendar (optional)

Some tools show a monthly calendar with the phase for each day, plus the upcoming notable phases like full moon and new moon dates.

Apply to plans

Use the result for stargazing (new moon is best), photography, fishing or hunting where the lunar effect matters, cultural and religious events, or simple curiosity.

When to Use Moon Phase Calculator

Astronomy hobbyists

Tracking moon phases shapes stargazing plans, telescope viewing, and astrophotography. Full moons wash out deep-sky objects; new moons make them visible. Amateur astronomers and night photographers both plan around the lunar cycle.

Wildlife and fishing

Many species behave differently across the lunar cycle. Fishing tends to be best around new and full moons, and wildlife watching benefits from full moons when nocturnal animals are more active. Anglers, naturalists, and hunters all use this kind of timing.

Cultural and religious dates

Many holidays follow lunar cycles. Easter falls on the first Sunday after the first full moon after the spring equinox; Ramadan follows the lunar month; Chinese New Year tracks the new moon. The tool helps determine these dates and supports religious scheduling and cultural events.

Educational and curiosity

Understanding the lunar cycle and its eight phases — new, waxing crescent, first quarter, waxing gibbous, full, waning gibbous, last quarter, waning crescent — comes naturally when you can see them mapped to specific dates. Students and educators use the tool that way.

Moon Phase Calculator Examples

Today's phase

Input

Today's date

Output

Phase: Waxing Gibbous (75% illuminated). Days since new moon: 11. Next full moon: 4 days.

A standard lookup. The tool calculates the phase from the date and reports the phase name, illumination percentage, the day count within the current cycle, and the distance to the next major phase.

Specific date

Input

December 25, 2024

Output

Phase: Waning Crescent (10% illuminated). Old moon visible early morning.

Historical or future dates work the same way. The tool fits planning observations, historical research into lunar conditions on specific dates, and event planning.

Phase calendar

Input

Month view of December 2024

Output

Visual calendar with moon phase for each day. New, first quarter, full, last quarter highlighted.

A calendar view supports monthly planning, photography scheduling, and identifying full moon dates ahead of time.

Tips & Best Practices for Moon Phase Calculator

1.Moon phases are predictable. The cycle is roughly 29.5 days from new moon to new moon, and the calculations are very accurate with no major variation.
2.Moonrise and moonset times vary by location. A phase calculator usually shows the phase rather than the exact rise and set times — use an astronomy app like Stellarium for visibility times.
3.The best stargazing happens around the new moon. The sky is darkest, deep-sky objects are visible, and observation plans should be built around that window.
4.Full moons can affect sleep. Some studies suggest reduced sleep quality during a full moon, so plan accordingly if you are sensitive to it.
5.Lunar eclipses differ from regular phases. An eclipse is a special event when a full moon enters Earth's shadow, separate from the normal phase calculation.
6.Phases look reversed between hemispheres. A waxing crescent in the Northern Hemisphere appears like a waning crescent in the Southern. The tool accounts for this, but verify if it matters for your case.

Frequently Asked Questions

There are eight phases. New Moon is invisible; Waxing Crescent is growing from 1 to 49 percent illuminated; First Quarter is 50 percent illuminated; Waxing Gibbous grows from 51 to 99 percent; Full Moon is 100 percent; Waning Gibbous shrinks from 99 down to 51 percent; Last Quarter is 50 percent; Waning Crescent shrinks from 49 down to 1 percent. The full cycle takes about 29.5 days.

Moon Phase Calculator

Select Date

Waning Crescent

Upcoming Phases

Lunar Cycle Progress

About Moon Phase Calculator

How to Use Moon Phase Calculator

Pick a date

View phase details

Browse calendar (optional)

Apply to plans

When to Use Moon Phase Calculator

Astronomy hobbyists

Wildlife and fishing

Cultural and religious dates

Educational and curiosity

Moon Phase Calculator Examples

Today's phase

Specific date

Phase calendar

Tips & Best Practices for Moon Phase Calculator

Frequently Asked Questions

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