Just fill out the "list of dates" box (down below) with the dates of every new moon you can keep track of. Separate the dates with an ENTER. The "output" window will automatically calculate the averages, errors, dates, and predict the next new moon. You can scroll through the math if you think there might be a mistake.

Some suggestions:

- At least five dates are recommended. More data = more accurate predictions.

- Try to pick a consistent "start time". Since the moon's phases last multiple days, people usually consider the "first visible sign" to be "day 0". It doesn't really matter as long as you're consistent, though.

- Don't worry about missing any dates, this program will detect and skip the gaps.

( your list of dates goes here, YYYY/MM/DD, no spaces )

Attempt to fix date formatting (might not work)

Expected Cycle Time (just guess):

( this bit gets filled automatically whenever you change the input )

( numbers will fill in here )

Have you ever wanted a free, open-source, simple tool for tracking the Moon? Of course you have!

It sucks that there are so many moon-trackers nowadays that are stuck behind paywalls. Knowing the phases of the moon, knowing when phases will happen, and knowing that the moon isn't being tracked by some dataseller somewhere should be a right, in my opinion.

Someone very dear to my heart wanted a way to track the moon, so I made a little Excel spreadsheet. It worked really well, but it was clunky, so I figured I'd redo it in Javascript for the browser... Having a nice GUI sure helps.

This page performs all calculations inside the browser, completely offline, and doesn't save anything, not even any cookies. You'll need to copy and paste your input somewhere safe, or it'll be gone next time you refresh.

All this site mathematically does is use a normal distribution (aka "the bell curve") to extrapolate from the set of dates you give it. It's been filled out with some example dates, so you can get the idea of how it works. This works very well, however, it's just not possible to predict any more accurately than a few days.

This page is contained in a single HTML file, so you can download it and use it offline, at any time. If that link doesn't work, you can probably just right-click anywhere and click "Save As".

This page is licensed under GNU GPL-V3. I am, by no means, an expert in medicine, law, or HTML; if you are, and you have any ideas/corrections/fixes/complaints, head over to the GitHub.