# Moon Phase Calculator

Find the moon phase for any date from 1900 to 2100. See if it's a new moon, full moon, quarter, crescent, or gibbous with illumination percentage.

## What this calculates

Pick any date and find out what the moon looks like. This calculator tells you the exact phase, how much of the moon is illuminated, and when the next full moon and new moon will happen. Great for photographers, gardeners, and anyone who just loves looking up.

## Inputs

- **Year** — min 1900, max 2100
- **Month** — min 1, max 12
- **Day** — min 1, max 31

## Outputs

- **Moon Phase** — formatted as text
- **Illumination** — formatted as text
- **Days into Cycle**
- **Days until Next Full Moon**
- **Days until Next New Moon**

## Details

The moon goes through a complete cycle every 29.53 days (called the synodic month). The eight phases are:

  - New Moon -- 0% illuminated, invisible

  - Waxing Crescent -- 1-49% illuminated, growing

  - First Quarter -- 50% illuminated (right half)

  - Waxing Gibbous -- 51-99% illuminated, still growing

  - Full Moon -- 100% illuminated

  - Waning Gibbous -- 99-51% illuminated, shrinking

  - Last Quarter -- 50% illuminated (left half)

  - Waning Crescent -- 49-1% illuminated, almost gone

How the Calculation Works

We use a known new moon date (January 6, 2000) as our reference point. By calculating the number of days between that reference and your chosen date, then dividing by the synodic month (29.530588853 days), the remainder tells us where we are in the current lunar cycle.

This method is accurate to within a few hours for dates in the 1900-2100 range. For precise astronomical calculations, factors like lunar orbit eccentricity and solar perturbations would need to be included.

## Frequently Asked Questions

**Q: How accurate is this moon phase calculator?**

A: This calculator is accurate to within a few hours for dates between 1900 and 2100. It uses the synodic month (29.530588853 days) and a reference new moon from January 6, 2000. Professional astronomical calculations include additional orbital corrections, but for identifying the phase on any given day, this method is reliable.

**Q: What is a synodic month?**

A: A synodic month is the time it takes for the moon to go from one new moon to the next, which is 29.530588853 days (about 29 days, 12 hours, and 44 minutes). This is different from the sidereal month (27.32 days), which is the time for the moon to orbit Earth relative to the stars.

**Q: Why does the moon have phases?**

A: Moon phases happen because we see different amounts of the moon's sunlit side as it orbits Earth. When the moon is between Earth and the Sun, we see the dark side (new moon). When Earth is between the moon and Sun, we see the fully lit side (full moon). The phases in between show partial illumination.

**Q: Does the moon phase affect gardening?**

A: Many gardeners follow lunar planting calendars. The general tradition is to plant above-ground crops during the waxing moon (new to full) and root crops during the waning moon (full to new). Scientific evidence is limited, but the practice has centuries of history across many cultures.

**Q: How often is there a full moon?**

A: There's a full moon about every 29.5 days, which means most months have one full moon. Occasionally a month will have two full moons, and the second one is called a "blue moon." This happens roughly every 2.5 years.

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Source: https://vastcalc.com/calculators/everyday/moon-phase
Category: Everyday Life
Last updated: 2026-04-08