Date Calculators
Date questions seem simple until you hit leap years, month ends, and conventions: is the end date included? Which week-numbering standard? These calculators state the rules they use on every page, use calendar arithmetic that never divides elapsed milliseconds by 86,400,000 (which breaks across daylight saving changes), and handle February 29 and year boundaries correctly.
Date Difference Calculator
Break down the gap between two dates into years, months and days.
Days Between Two Dates
Count calendar days between dates, with business-day breakdown.
Days Until a Date
Count down the days from today to any future or past date.
Add Days to Date
Add or subtract days, weeks, months or years from any date.
Age Calculator
Calculate exact age in years, months, and days plus next birthday countdown.
Business Days Calculator
Count business days between dates or add working days to a date.
Week Number Calculator
Find the ISO 8601 week number and week year for any date.
Day of the Week Finder
Find which day of the week any past or future date falls on.
Leap Year Checker
Check whether a year is a leap year with the rules explained.
When to use these tools
- Counting down to deadlines, launches, and events
- Computing exact age in years, months, and days
- Working out business days for payroll, SLAs, and delivery estimates
- Finding ISO week numbers for planning and reporting
Frequently asked questions
Does “days between dates” include both endpoints?
How are business days defined here?
Which week numbering is used?
Other categories
Timestamp Tools
Convert Unix timestamps, epoch seconds, and milliseconds to and from human dates.
Time Converters
Switch between 12-hour, 24-hour, and military time formats instantly.
Time Zone Tools
Convert times across IANA time zones, run a world clock, and plan meetings.
Timers
Countdown timer, stopwatch, and Pomodoro sessions that stay accurate.
Work & Hours Tools
Shift durations with breaks, overnight handling, and decimal hours.