How this works
Enter the values shown, review the result, and verify assumptions before acting. The calculation is performed on your device without uploading these entries.
Compare two dates by elapsed UTC calendar days. The input fields are labeled with the units or formats used in the calculation. Change one value at a time to see how the result responds, and compare the output with the worked example below.
Formula or method
The method above describes the calculation or algorithm being used by this browser utility. It is shown so you can understand the result, check assumptions and repeat the calculation independently if needed.
Worked example
October 1 to October 11 spans 10 calendar days.
Limitations and accuracy
This is calendar-day math, not business-day counting.
The calculation runs locally in your browser. No result is guaranteed to be suitable for financial, legal, medical, or safety-critical decisions. Check independent authoritative sources in those cases.
More context
Daylight length varies with latitude and season because Earth’s axis is tilted. A simple astronomical formula can estimate day length from solar declination and latitude, but terrain, atmospheric refraction and observer elevation change observed sunrise and sunset. Solar noon is related to longitude, not necessarily 12:00 on a civil clock; time zones and daylight saving add more differences.