What this calculator does
Moon phase finder works out the approximate Moon phase on any date, from the lunar synodic cycle. Enter your own figures above and the answer updates as you type: nothing is fixed in the code, so the result reflects exactly the numbers you supply.
The formula this calculator evaluates is printed under the tool and explained below, so you can check the working by hand or reuse it in a spreadsheet.
The formula
FormulaAge = days since a known new moon, mod 29.53058770576-day synodic month
The inputs explained
| Field | What to enter |
|---|---|
| Date | A calendar date. |
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
Examples across different dates
The same calculation at a range of dates, with every other input held at its starting value. These are generated relative to the day the page was built.
Examples across different dates
| Date | Moon phase | Age of the cycle | Approx. illumination |
|---|---|---|---|
| 2026-08-11 | Waning Crescent | 26.8 days | 8.26% |
| 2026-09-03 | Waning Gibbous | 20.3 days | 69.5% |
| 2026-11-02 | Last Quarter | 21.2 days | 60.5% |
| 2027-01-31 | Last Quarter | 22.6 days | 45.6% |
| 2027-08-04 | New Moon | 0.9 days | 0.900% |