Moon Phase Calculator
Pick a date to see the moon phase, how much of it is lit and the next full moon.
What this tool does
The moon takes about 29.53 days to go from one new moon to the next. Count the days since a known new moon (6 January 2000) and divide out whole cycles to get the moon's age: age 0 is a new moon, about 7.4 days is first quarter, 14.8 days is full moon. Pick a date above to see the phase and the next full moon.
Calculates the moon's age from the average lunar month.
Names the phase, estimates the lit fraction and the dates of the next full and new moon.
How to use it
- Pick a date (today by default).
- Read the phase name, age and illumination.
- See the dates of the next full and new moon.
- Try your birthday or an event date.
Why use this calculator
Finds the phase of the moon for any date from the average length of the lunar month, with the moon's age in days, the percentage lit and the dates of the next full and new moon. Gardeners, photographers, anglers, campers and curious people want to know the moon phase for a date. A formula gives an answer for any date without looking up a table.
Why we built it
We built the moon phase calculator to give the phase, age, illumination and the next full and new moon for any date, with the accuracy stated honestly. Plan the date with the days until calculator and see signs with the zodiac sign calculator.
Who this tool is for
- Photographers and stargazers
- Gardeners and anglers who follow the moon
- Anyone curious about the moon on a special date
When to use it
- Planning night photography, stargazing or camping.
- Checking the moon on your birthday or a wedding date.
- Tide, fishing and gardening plans that follow the moon.
- Teaching how the lunar cycle works.
How it works
The synodic month, from new moon to new moon, averages 29.530588853 days. The reference new moon is 6 January 2000 at about 18:14 UTC. The moon's age is the days since then, modulo one cycle. The lit fraction is (1 − cos(2π × age ÷ 29.53)) ÷ 2, and the phase name comes from dividing the cycle into eight equal parts.
Example: on 21 January 2000 the age is about 14.9 days, which is a full moon, 100% lit. The next full moon is about 19 February 2000.
The real month varies by several hours around the average, so the result is accurate to about a day. For exact moonrise or eclipse times, use an astronomical almanac.
A worked example
These are the values the calculator opens with, so you can see exactly what it does with them. Change any value on the page and the result updates; the figures below come from the same calculation.
| Input | Value |
|---|---|
| Date | 2026-03-15 |
With those inputs, the calculator returns:
- Moon phase: Waning Crescent
- Age of the moon: 26.5 days
- Illuminated: 10%
- Next full moon (about): Thursday, 2 April 2026
- Next new moon (about): Wednesday, 18 March 2026
- Cycle length used: 29.530588853 days
What you give it, and what you get back
| Item | Details |
|---|---|
| Date | Any date. The calculation uses noon UTC on that day. |
| Output | Phase name, age in days, percent illuminated, next full moon, next new moon. |
Issues you may run into
| What you see | Why it happens | What to do |
|---|---|---|
| Phase differs from a lunar calendar by a day | Real phase times vary around the average. | Use an almanac for exact times. |
| Illumination is not what I see | It is the geometric lit fraction. | Clouds, horizon and libration change what you see. |
| Southern hemisphere view | The phase is the same everywhere, but the moon looks flipped. | The lit side appears on the opposite side. |
Assumptions and limitations
- Average-month method, about ±1 day.
- No moonrise, moonset or eclipse times.
Frequently asked questions
How is the moon phase calculated?
From the number of days since a known new moon, divided into the average 29.53-day lunar cycle.
How accurate is it?
Within about a day. Exact times need an almanac.
What is the moon phase on my birthday?
Enter your birth date above.
How long is a lunar cycle?
About 29.53 days from new moon to new moon.
What is moon illumination?
The fraction of the moon's visible disc that is lit by the sun.
Is my information sent anywhere?
No. The calculation runs in your browser and nothing leaves the page.