Date calculations look simple until month ends, leap years, weekends or different formats become involved. Bethemesh’s Date & Time family separates these problems into focused tools so calendar arithmetic is not confused with plain duration arithmetic.
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Date and time calculations: a practical guide
Date differences, durations, business days, ISO weeks, recurrences and formats: choose the right date and time calculation.
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Date difference or time duration?
Use the date difference calculator to compare calendar dates in years, months, days and total days. For a work shift or clock interval, the time duration calculator is more appropriate and can handle a period crossing midnight.
The duration converter converts values between milliseconds, seconds, minutes, hours, days and weeks. Those are arithmetic conversions; they do not replace calendar calculations when real month lengths matter.
Add or subtract from a date
The date arithmetic calculator adds or subtracts days, months or years while keeping month-end cases valid. The days until date calculator measures a countdown or elapsed days, while the age calculator applies calendar logic to a birth date and reference date.
Business days, ranges and recurrences
Calendar days and business days answer different questions. The business days calculator excludes weekends and can shift a date by a number of working days. The date range generator builds dates between two boundaries, while the recurring dates generator creates a sequence at a chosen frequency.
These tools are useful for schedules, deadlines and recurring plans without building spreadsheet formulas.
Locate a date in the calendar
The ISO week calculator returns the week number and ISO week-year, which can differ from the calendar year around New Year. The day of week calculator identifies the weekday, while the day of year calculator returns its position from 1 to 365 or 366.
Formats, timestamps and relative time
The date format converter presents the same date in several readable formats. The Unix timestamp converter works with a numeric representation of an instant and includes ISO 8601 output. The relative time calculator turns an interval into a human-oriented expression such as “in 3 days” or “2 hours ago”.
All these calculations run locally in your browser. Your dates do not need to be uploaded to Bethemesh.
For international scheduling, continue with the guide to time zones, daylight saving time and meetings.
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Sources and references
- ISO — ISO 8601 Date and time format (opens in a new tab)Page in English