How the calculations work

Days and sleeps

A countdown excludes today and includes the target date. September 19 to December 25, 2026 is 97 days, or 13 weeks and 6 days. Sleeps means the same number of calendar nights. Weekdays means Monday through Friday and does not remove holidays.

Dates between two days

The date difference calculator includes the earlier date and excludes the later one. Its include-end-date choice counts both. February 28 to March 1, 2024 is 2 days, or 3 when both dates count. Reversing the dates gives the same magnitude with a minus sign.

Months, years and age

Adding a month keeps the day where possible. January 31 plus one month in 2028 becomes February 29. Age counts completed years, then completed months, then days. February 29 birthdays use February 28 in other years. This arithmetic is not a legal-age ruling.

Working days

Choose a country or region calendar to remove its published holidays as well as the selected weekends. Actual holiday dates and observed closures can differ. The exclusion list shows which dates were removed. Local, employer and special closures can add exceptions.

Time zones and clock changes

A calendar day and 24 elapsed hours are different questions. In New York, March 8, 2026 at 1:30 AM to 3:30 AM is one elapsed hour because the clock jumps forward. A nonexistent local time is rejected; if a time occurs twice, choose its earlier or later occurrence. The timezone converter keeps the instant while changing the local display.

Week numbers and Julian dates

ISO weeks start Monday; week one contains the first Thursday. The Sunday-start comparison uses the week containing January 1. The Julian Date converter distinguishes the Julian calendar, astronomical Julian Date and ordinal day of the year. Julian Dates begin at noon; Modified Julian Date subtracts 2,400,000.5.

Sun, Moon and eclipses

Moon phases and seasons use US Naval Observatory times to the published minute. Solar times and eclipse maxima use astronomical calculations. A sunrise location is one representative point, not a promise about every address in an area. The horizon, terrain, weather and elevation can change visible rise and set times. Global eclipse maxima are not local viewing circumstances.

Publishers, update dates and required credits are on the Sources page linked below.