A tool that starts from the new moon you already have
Moon age counts how many days have passed since the new moon, and it is the number photographers and campers reach for when they want to know how bright the sky will be. This page takes the new moon date printed in the calendar or almanac you are already reading, plus its time if you know it, and counts from there. For example, the December 2026 new moon falls around 7:52 p.m. EST on December 8. With the page defaults, reference 2026-12-08 at 19:52 and target date 2026-12-09, the tool shows a moon age of 0.7 days, the next full moon on 2026-12-23 and the next new moon on 2027-01-07 (Eastern Time), which match published tables. Enter reference 2026-10-10 at 11:50 (EDT) with target date 2026-10-11 instead and the next full moon shows as 2026-10-25, while the actual full moon falls at 12:11 a.m. EDT on October 26, a live example of the ±1 day error that the mean cycle carries. A reference close to your target date works best.
How the 29.530589-day mean month is used
The days elapsed from the reference new moon instant to noon on the target date are divided by the mean synodic month of 29.530589 days, and the remainder is the moon age. The next full moon is the reference instant plus half a cycle, the next new moon plus one cycle, and the page shows the calendar date each predicted instant lands on. A blank time is treated as 12:00, the middle of the day. Anchoring at midnight and rounding down would run about half a day early on average, sometimes more than a full day. The illuminated fraction is a cosine approximation.
Accuracy and what this page does not do
Because the Moon's orbit is elliptical, a real lunation runs anywhere from about 29.18 to 29.93 days, and actual new and full moon instants stray up to roughly ±14 hours from the mean. Treat every listed date as accurate to ±1 day (as of October 2026). Times are in whatever local time zone you used for the reference. Moonrise and moonset depend on your latitude and longitude, so they are not calculated here. For exact instants, use the U.S. Naval Observatory or NASA moon phase tables.
Frequently Asked Questions
Use the new moon closest before your target date, which keeps the error smallest. If your calendar or almanac lists the time, enter it in your local time; if not, leave it blank and the page uses 12:00.
The page uses the 29.530589-day mean synodic month. Because the lunar orbit is elliptical, actual new and full moon instants stray up to about ±14 hours from the mean, so a date near midnight can flip by one day. That is why results are shown as ±1 day.
No. Moonrise and moonset need the latitude and longitude of your location, so this page only reports moon age, phase name, illuminated fraction and estimated full and new moon dates.