Moon Phase Calculator – Check Lunar Phases by Date
Estimate the phase of the moon on any date.
About the Moon Phase Calculator
What is the Moon Phase Calculator?
A moon phase calculator estimates the phase and illuminated fraction of the moon for any date.
Why use this calculator?
Photographers, astronomers, gardeners and anyone curious about the night sky use moon phases to plan and to understand the lunar cycle.
How to use it
- Enter a date.
- Read the named phase and the illumination percentage.
Formula
The phase is based on the synodic month of about 29.53 days since a known new moon.
This is a simplified mean-cycle estimate; the true phase can differ by a few hours.
Frequently Asked Questions
How accurate is this?
It uses the average lunar cycle, so it can be off by up to about half a day. For precise astronomy, use an ephemeris.
How long is a lunar month?
From one new moon to the next takes about 29.53 days on average.
Does it account for leap years?
Yes. The date logic follows the Gregorian calendar, including leap years and differing month lengths.
Are weekends and holidays excluded?
Only if the calculator says so. By default, results count every calendar day; use a business-day option where available.
Which time zone is used?
Calculations use whole calendar dates and are time-zone independent unless a time-of-day is involved.
Is this calculator free to use?
Yes. Every calculator on this site is completely free, with no hidden fees, no subscriptions and no limits on how many times you can use it.
How accurate are the results?
We use standard, widely accepted formulas and calculate in your browser using double-precision arithmetic. Results are rounded for readability, so treat them as reliable estimates rather than a guarantee. Real-world factors can vary the true figure.
Can I add this calculator to my own website?
Yes. Open this calculator page and use the "Add to your website" box in the sidebar to copy a ready-made iframe snippet, then paste it into any HTML page.
Does it work on a phone or tablet?
Yes. The layout is fully responsive, so it works on desktops, laptops, tablets and mobile phones, and every input adapts to touch screens.
Is the information I type kept private?
Yes. All calculations run locally in your browser. Nothing you enter is uploaded, stored or shared with anyone.