Moon Phase Calculator
Phase, illumination, and days to next full moon
Use this when you need a fast, accurate result — no sign-up, works entirely in your browser.
Moon phase—
Illumination (%)—
Moon age (days)—
Days until next full moon—
How to Use
- Enter your details into the fields above.
- Click the calculate button to get your result instantly.
- Use the clear button to start a new calculation.
Example
- 2026-09-09 → Waxing Crescent, 17.5% illuminated, moon age 4.06 days, next full moon in 11 days
- 2026-09-17 → Waxing Gibbous, 91.9% illuminated; full moon in ~3 days
Formula
Moon age = (days since the 1970-01-01 new moon) mod 29.530588853, the mean synodic month. Illumination = (1 − cos(2π × age / synodic)) / 2. Eight phases are mapped across the cycle. This is a mean-moon approximation, so it can be off by several hours from an exact ephemeris.
About Moon Phase Calculator
Phase, illumination, and days to next full moon. This free online tool gives you fast, accurate results without registration or downloads.
Everything runs locally in your browser, so your data is never uploaded or stored — privacy first.
Frequently Asked Questions
Is this tool free to use? +
Yes, it is completely free with no registration or download required.
Is my data private? +
Yes. Everything is processed locally in your browser. Nothing is uploaded or stored on our servers.
Does it work on mobile? +
Yes, it works on any device — phone, tablet, or desktop.