Moon Phase Calculator
Fill in the value and the answer updates as you type.
How the Moon Phase Calculator works
The Moon cycle (synodic month) lasts 29.530589 days. The age is the number of days since a reference new moon on 6 January 2000, taken modulo that length. Illumination = (1 − cos(2π × age ÷ cycle length)) ÷ 2. The phase names follow the age. This mean-cycle method is typically accurate to within a day because the real orbit is not perfectly regular. Example: with Date 2026-10-07, the result is Moon phase = Waning Crescent; Moon age (days since new moon) = 25.6; Illuminated part of the disk (%) = 16.1.
Inputs and results
The Moon Phase Calculator takes 1 input and gives 4 results.
What you enter
- Date — starts at 2026-10-07.
What you get
- Moon phase
- Moon age (days since new moon)
- Illuminated part of the disk (%)
- Days until the next full moon
Moon Phase Calculator FAQ
How do I use the Moon Phase Calculator?
Enter date in the fields, then read moon phase, moon age (days since new moon), illuminated part of the disk (%) and days until the next full moon in the result panel. The answer updates as you type, and you can press Calculate or Enter to refresh it. Use “Copy link” to share your exact numbers with someone else.
What does the Moon Phase Calculator calculate?
Moon phase, age, and illumination for any date. It returns moon phase, moon age (days since new moon), illuminated part of the disk (%) and days until the next full moon from the 1 value you provide.
What values does the Moon Phase Calculator start with?
It opens with date 2026-10-07 so you can see a working result straight away. Replace them with your own numbers, or press Reset to return to these starting values.
Is the Moon Phase Calculator free and private?
Yes. It is free, needs no account, and runs in your browser, so nothing you type is sent to or stored on our servers. See the Privacy Policy for details.
Can I rely on the Moon Phase Calculator for important decisions?
Treat the result as a well-rounded estimate. Real situations often have details a general calculator cannot know, so confirm important decisions with a qualified professional. See the Disclaimer for more.