Moon Phase Calculator
Moon Phase Calculator
Choose any date — past, present, or future — to see its lunar phase.
Southern Hemisphere observers see the Moon's illuminated limb on the opposite side.
Select a Date to See the Moon Phase
Choose any date using the date picker and click Calculate Phase to see the lunar phase, illumination, cycle progress, upcoming phases, and practical guidance.
Find the lunar phase for any date — past, present, or future
The Moon has guided human civilizations for thousands of years. From ancient agricultural societies planning their harvests to modern gardeners timing their planting, understanding lunar phases has practical significance that spans cultures and centuries. Our Moon Phase Calculator gives you instant, accurate information about the lunar cycle for any date you choose — whether you're looking up today's phase, planning around an upcoming full moon, or curious about what phase illuminated the sky on a historical date. The Moon travels through a complete cycle of phases approximately every 29.53 days — a period called the synodic month. This cycle begins at the New Moon, when the Moon is positioned between Earth and the Sun and its illuminated face is turned entirely away from us, leaving only a dark disk in the sky. As the Moon orbits Earth, sunlight progressively illuminates more of its visible surface. We see a thin crescent emerge on the right side (in the Northern Hemisphere) during the Waxing Crescent phase, then half the Moon's face lights up at the First Quarter. The illuminated portion continues to grow — waxing — through the Waxing Gibbous phase until finally, at the Full Moon, we see the entire face of the Moon bathed in sunlight. After that, the illumination decreases — waning — through Waning Gibbous, Last Quarter, and Waning Crescent, before the cycle resets at New Moon again. Our calculator uses precise astronomical algorithms derived from Julian Day Number calculations and a well-established reference point: the known New Moon of January 6, 2000. By computing how many days have elapsed since that reference event and dividing by the synodic month period, we determine exactly where in the lunar cycle any given date falls. This gives you the moon age in days, the phase name from the standard set of eight recognized lunar phases, and the illumination percentage — a measure of how much of the Moon's disk is lit as seen from Earth. The illumination is calculated using a cosine function that models the geometry of sunlight falling on the lunar surface. Beyond the basic phase data, our calculator provides a rich set of practical insights. The lunar cycle progress ring shows you at a glance where today sits within the 29.53-day cycle. The upcoming phases panel lists the next New Moon, First Quarter, Full Moon, and Last Quarter — complete with exact dates so you can mark your calendar. If the selected date is a Full Moon, you'll see its traditional folk name: January's Full Moon is called the Wolf Moon, February's is the Snow Moon, and so on through the year, with each month's Full Moon carrying names rooted in Native American and colonial American traditions that reflect seasonal activity or natural phenomena of that time of year. The calculator also checks for special lunar events. A Supermoon occurs when a Full Moon coincides with the Moon being near its closest approach to Earth (perigee), making it appear slightly larger and brighter than usual. A Micromoon is the opposite — a Full Moon near apogee, the Moon's farthest point. A Harvest Moon is the Full Moon nearest to the autumnal equinox in September, traditionally the brightest Full Moon of harvest season. For gardeners and farmers, lunar gardening practices have been observed for centuries. The principle is straightforward: during waxing phases, as the Moon grows toward Full, moisture and sap in plants are thought to rise, making it a good time to plant above-ground crops, leafy greens, and fruits. During waning phases, as the Moon shrinks toward New, energy is said to move downward into the roots — an ideal time for planting root vegetables, bulbs, and perennials, as well as for weeding and pruning. Whether you take this as folk wisdom or practical tradition, many experienced gardeners swear by timing their planting with the Moon. Fishers and hunters have similarly observed that fish and game tend to be more active around Full and New Moons, when gravitational tidal forces are strongest. Our fishing activity rating gives you a simple percentage score for each phase, reflecting the historical observation that biting activity peaks at Full Moon and decreases through the quarter phases. Use this alongside local tide tables and seasonal patterns for the best results. The hemisphere toggle accounts for the fact that observers in the Southern Hemisphere see the Moon's illuminated limb on the opposite side compared to Northern Hemisphere observers. While the phase calculations are the same, the visual orientation of the crescent or gibbous shape is mirrored — in Australia, the crescent opens to the left during waxing. Our moon visual flips accordingly when you select Southern Hemisphere. Select your date, choose your hemisphere, and explore everything our Moon Phase Calculator has to offer.
Understanding Lunar Phases
What Are Moon Phases?
Moon phases are the cyclically changing illumination of the Moon's visible surface as seen from Earth. The Moon itself does not emit light — it reflects sunlight. As the Moon orbits Earth, different portions of its sunlit face are visible to us, creating the appearance of waxing (growing) and waning (shrinking) illumination. The eight standard phases recognized by astronomers and popularized in calendars are: New Moon, Waxing Crescent, First Quarter, Waxing Gibbous, Full Moon, Waning Gibbous, Last Quarter, and Waning Crescent. The complete cycle takes approximately 29.53 days — the synodic month — from one New Moon to the next. This differs slightly from the sidereal month (27.32 days), which measures the Moon's orbital period relative to distant stars, because Earth itself is also orbiting the Sun during that time.
How Are Phases Calculated?
Phase calculation relies on determining the Moon's 'age' — the number of days elapsed since the most recent New Moon. Our calculator uses the Julian Day Number (JDN) system, a continuous count of days since January 1, 4713 BCE, to avoid calendar complexities. We convert your input date to a JDN, subtract the JDN of a known reference New Moon (January 6, 2000 at 18:14 UTC, JD 2451549.2597), and find the remainder when dividing by the synodic month period of 29.53058770576 days. This remainder is the moon age. The illumination percentage is then calculated as: illumination = (1 − cos(2π × age / synodic_month)) / 2 × 100. The phase name is assigned based on which eighth of the cycle the age falls into, with each eighth spanning approximately 3.69 days.
Why Do Moon Phases Matter?
Moon phases have influenced human behavior across virtually every culture throughout history. Ancient calendars were lunar or lunisolar, and many religious and cultural festivals are still scheduled by the Moon — from the Islamic Ramadan and Eid to the Jewish Passover, Easter, and Chinese New Year. Ecologically, moon phases drive oceanic tides through gravitational interaction, and many marine organisms — from corals that spawn at full moons to crabs that molt with tidal cycles — have life cycles synchronized with the lunar month. For night-sky observers, knowing the moon phase is essential: a bright full moon washes out faint galaxies and nebulae, while a new moon offers the darkest skies for deep-sky observation. Gardeners, farmers, and fishers worldwide use lunar cycles to guide planting and activity, with research suggesting some biological merit to these ancient practices.
Limitations of This Calculator
Our Moon Phase Calculator uses a simplified Julian Day approach that is accurate for most everyday purposes, providing moon age and phase name within a fraction of a day. However, for professional astronomical work, the Jean Meeus method with full polynomial corrections (accounting for solar and lunar anomaly, argument of latitude, and DeltaT corrections) provides higher precision. Moonrise and moonset times require your specific geographic latitude, longitude, and timezone — calculations that depend on local horizon geometry and atmospheric refraction. We do not currently provide location-dependent rise/set times, which would require an external geocoding API. Supermoon detection uses an approximated distance model rather than precise orbital elements, so edge cases near the threshold may not be perfectly classified. For critical applications — eclipse prediction, navigation, or scientific research — consult the U.S. Naval Observatory or JPL Horizons ephemeris system.
Formulas
Converts a calendar date (year Y, month M, day D, UT in hours) to a continuous day count used for astronomical calculations. This removes calendar irregularities and makes it easy to compute elapsed time between any two dates.
Calculates the number of days since the most recent New Moon by taking the remainder after dividing the elapsed days from a known reference New Moon (January 6, 2000 at 18:14 UTC) by the synodic month period.
Models the fraction of the Moon's visible disk that is illuminated using a cosine function. At New Moon (age = 0), illumination is 0%. At Full Moon (age ~ 14.77), illumination reaches 100%.
Reference Tables
Eight Lunar Phases
| Phase | Moon Age (days) | Illumination | Visibility |
|---|---|---|---|
| New Moon | 0 - 1.85 | 0% | Not visible |
| Waxing Crescent | 1.85 - 5.53 | 1 - 49% | Afternoon to evening |
| First Quarter | 5.53 - 9.22 | 50% | Noon to midnight |
| Waxing Gibbous | 9.22 - 12.91 | 51 - 99% | Afternoon to early morning |
| Full Moon | 12.91 - 16.61 | 100% | Sunset to sunrise |
| Waning Gibbous | 16.61 - 20.29 | 99 - 51% | Evening to morning |
| Last Quarter | 20.29 - 23.99 | 50% | Midnight to noon |
| Waning Crescent | 23.99 - 29.53 | 49 - 1% | Pre-dawn to morning |
Traditional Full Moon Names
| Month | Name | Origin |
|---|---|---|
| January | Wolf Moon | Howling wolves in winter |
| February | Snow Moon | Heavy snowfalls |
| March | Worm Moon | Thawing ground, earthworms return |
| April | Pink Moon | Wild pink phlox blooms |
| May | Flower Moon | Abundant spring flowers |
| June | Strawberry Moon | Strawberry harvest season |
| July | Buck Moon | Deer antler growth |
| August | Sturgeon Moon | Great Lakes sturgeon fishing |
| September | Harvest Moon | Bright light for harvesting |
| October | Hunter's Moon | Fattened game, hunting season |
| November | Beaver Moon | Beaver trapping season |
| December | Cold Moon | Onset of deep winter cold |
Worked Examples
Finding the Moon Phase for July 20, 1969 (Apollo 11 Landing)
Convert July 20, 1969 to Julian Day Number: JDN = 2440423.5
Calculate elapsed days from reference New Moon: 2440423.5 - 2451549.2597 = -11125.7597
Find moon age: -11125.7597 mod 29.53058770576 = 5.31 days
Map 5.31 days to phase: falls in Waxing Crescent range (1.85 - 5.53)
Calculate illumination: (1 - cos(2pi x 5.31 / 29.53)) / 2 x 100 = 28.5%
Determining the Next Full Moon from March 1, 2025
Convert March 1, 2025 to JDN: 2460735.5
Calculate moon age: (2460735.5 - 2451549.2597) mod 29.53 = 1.64 days
Full Moon occurs at moon age ~14.77 days
Days until Full Moon: 14.77 - 1.64 = 13.13 days
Add 13.13 days to March 1: March 14, 2025
How to Use the Moon Phase Calculator
Select Your Date
Click the date picker and navigate to any date — past, present, or future. The calculator works for historical dates stretching back centuries and future dates many years ahead. Today's date is pre-filled by default so you can immediately see the current lunar phase.
Choose Your Hemisphere
Select Northern or Southern Hemisphere. Observers in Australia, South America, and southern Africa see the Moon's illuminated crescent on the opposite side compared to those in North America or Europe. This toggle adjusts the moon visual accordingly while keeping the phase calculations identical.
Read Your Results
The results show the phase name with a CSS moon visual, illumination percentage donut chart, cycle progress ring, moon age in days, and the direction (waxing or waning). If the selected date is a Full Moon, you'll see its traditional folk name and any special designations like Supermoon or Harvest Moon.
Use the Practical Guidance
Scroll down to see upcoming phase dates so you can plan ahead, along with lunar gardening advice tailored to the current phase and a fishing activity rating based on gravitational tidal influence. Export your results to CSV for record-keeping or use the Print button for a clean hard copy.
Frequently Asked Questions
How accurate is this Moon Phase Calculator?
Our calculator uses the Julian Day Number method with a precise reference New Moon (January 6, 2000 at 18:14 UTC), providing phase name and moon age accuracy within a fraction of a day for dates ranging from ancient history to the distant future. For everyday purposes — gardening, photography planning, curiosity — this level of accuracy is more than sufficient. For professional-grade astronomical work requiring sub-second precision (such as eclipse prediction or satellite tracking), specialized software using the full Jean Meeus polynomial corrections or JPL ephemeris data is recommended. The illumination percentage is computed using a cosine model that closely matches observed values.
What is a Supermoon and how rare is it?
A Supermoon occurs when a Full Moon (or sometimes New Moon) coincides with the Moon being at or near perigee — its closest orbital point to Earth. At perigee, the Moon is roughly 356,500 km from Earth, compared to the average distance of 384,400 km. The result is a Full Moon that appears about 14% larger and 30% brighter than a Full Moon at apogee (farthest point). Supermoons occur roughly 3 to 4 times per year and are visible to the naked eye, though the size difference is often subtle without side-by-side comparison. The term was coined by astrologer Richard Nolle in 1979, but astronomers now use it widely. Some years bring multiple consecutive Supermoons as the perigee and full moon alignment persists for several cycles.
Why does the Southern Hemisphere see the Moon differently?
Earth's orientation means that observers in the Southern Hemisphere are looking at the Moon from the opposite direction compared to those in the Northern Hemisphere. While the phase itself — the amount of illumination — is identical worldwide, the orientation of the illuminated limb appears mirrored. In the Northern Hemisphere, the Waxing Crescent appears as a D-shape with light on the right. In the Southern Hemisphere, the same phase looks like a reverse-D or C-shape with light on the left. Similarly, the Full Moon appears 'upside down' relative to what Northern Hemisphere observers see. Our hemisphere toggle flips the moon visual (rotating it 180°) to accurately reflect the Southern Hemisphere perspective.
What are the traditional Full Moon names and where do they come from?
Traditional Full Moon names were used by Native American tribes and colonial Americans to track seasons and natural events. January's Wolf Moon references the howling wolves heard in the cold winter nights. February's Snow Moon reflects the heavy snowfalls of that month. March's Worm Moon marks the thawing ground and returning earthworms. April's Pink Moon is named after the pink wildflowers (phlox) blooming in spring. May's Flower Moon and June's Strawberry Moon continue the seasonal theme. July's Buck Moon refers to deer growing new antlers. August's Sturgeon Moon honored the abundance of that fish in the Great Lakes. September through December complete the cycle with Harvest, Hunter's, Beaver, and Cold Moons.
Does the Moon phase really affect fishing and gardening?
The Moon's gravitational influence on ocean tides is scientifically established, and the same forces affect freshwater bodies and potentially even soil moisture. Many experienced anglers report peak fish activity during Full Moon and New Moon phases when tidal forces are strongest and fish are more active feeding. Scientific studies have shown some correlation, though local conditions, temperature, and season typically outweigh lunar influence. For gardening, the biodynamic tradition (developed by Rudolf Steiner) and various folk traditions advocate planting by Moon phase, with some modern horticultural research finding modest support for root and leaf development differences between lunar planting periods. Whether scientific certainty or respected tradition, millions of gardeners worldwide plan by the Moon.
What is the difference between a synodic month and a sidereal month?
A sidereal month (27.32 days) is the time it takes the Moon to complete one orbit of Earth relative to distant background stars — a true orbital period. A synodic month (29.53 days) is the time between two consecutive identical phases, such as Full Moon to Full Moon. The synodic month is longer because while the Moon is orbiting Earth, Earth itself is moving around the Sun. By the time the Moon returns to the same position relative to the stars, Earth has moved about 27° along its orbit, so the Moon must travel that additional angular distance to again align with the Sun-Earth geometry and produce the same phase. This is why we experience 12 or 13 Full Moons per calendar year rather than the 13 complete sidereal orbits.