How to count calendar days, working days, and age
Worked examples for Toolora’s Age, Date, Days Between, and Working Days calculators — civil dates in the browser, not elapsed hours.
Age is not days divided by 365
A visa form that asks for age on 5 September 2026 wants completed years, leftover months, and leftover days on the civil calendar. Dividing days since birth by 365.25 is close for adults and wrong for leap-day birthdays and for infants. Toolora’s Age Calculator subtracts the birth date from an as-of date in your browser: it borrows days from the previous month when the as-of day-of-month is smaller, then borrows months from the year. Example: birth 1 January 2000, as of 5 September 2026 is 26 years, 8 months, and 4 days. Same-day birth and as-of is zeros. An as-of date before birth is rejected rather than shown as a negative age. Change as-of to a future wedding or school date when you need age on that day, not “today” on a server clock that might disagree with your timezone’s calendar date.
Adding a month is not adding 30 days
Date Calculator moves a start date by days, weeks, months, or years. Weeks are seven civil days including weekends. Months use the JavaScript calendar: 31 January plus one month overflows to early March in a common year, the same overflow most payroll software uses. Subtract walks backward with the same rules. Use this when you know a signature date and a duration (“ten calendar days after contract”) or a deadline and need the latest start. Do not use it to skip Saturdays — that is a working-day problem.
Signed days vs inclusive stays
Days Between Dates reports the signed difference between UTC midnights so a DST change does not add or drop a civil day. 1 January to 31 January is 30 days (boundaries crossed) and 31 inclusive dates if you count both endpoints. Same-day is 0 days and 1 inclusive date. A negative span means you typed end before start; swap the fields or take the absolute value. Hotels, visas, and “net 30” invoices disagree about endpoints — read both numbers instead of guessing.
Weekdays minus holidays you list
Working Days Calculator counts Monday–Friday in an inclusive range, then removes YYYY-MM-DD holidays you paste. It does not know national calendars. A Saturday holiday does not change the total; a Friday holiday does. January 2026 from the 1st through the 31st has 22 weekdays; excluding 1 January (a Thursday) leaves 21. Reverse the dates and the count is unchanged. Time of day is ignored. All four tools run locally — birthdays and holiday lists never leave the tab. Related: Time Zone Converter when the question is a wall clock, not a date.