Calculate the elapsed calendar days between employment dates, understand leap-year anniversaries, and choose the correct rule for inclusive days or workdays.
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The calculation
Elapsed calendar days = end date minus start date. Inclusive dates touched = elapsed days + 1 only when both endpoint dates count. Calendar years and weekdays are distinct representations.
Worked example
January 1, 2020 to January 1, 2021 is 366 elapsed days because 2020 includes February 29. It is also one calendar-year anniversary interval. If both endpoint date labels were days employed, 367 dates would be included instead.
The date difference E−S measures elapsed calendar-day boundaries. Employment policies may count the last date inclusively or count only scheduled working days; those require an explicit convention or calendar.
Video chapters
- 0:00 — Which duration do we mean?
- 0:11 — Subtract dates
- 0:25 — Count the leap year
- 0:40 — The worked answer
- 0:55 — Calendar year is a different unit
- 1:11 — Inclusive endpoint convention
- 1:29 — Workdays use a schedule
- 1:46 — Reusable method
Read the full transcript
How long has someone been employed? The answer depends on which dates you compare and what you mean by a day. We will measure the time between two dates first, then see why one calendar year can have three hundred sixty-six days.
Mark January first, twenty twenty as the start, and January first, twenty twenty-one as the end. Duration in elapsed calendar days is the end date minus the start date. Each step from one midnight to the next contributes one day.
Do not guess three hundred sixty-five. In twenty twenty, January contributes thirty-one days, and February contributes twenty-nine. The remaining months complete a leap year. That extra February day is part of the interval, so the twelve month lengths sum to three hundred sixty-six.
From January first to December thirty-first, three hundred sixty-five days have elapsed. Step one more date to January first, twenty twenty-one and the difference is three hundred sixty-six days. Add those days back to the start, and you land exactly on the end.
These two dates are also one calendar-year anniversary apart. A calendar year is not a fixed number of days: this one contains February twenty-ninth. Say one calendar year or three hundred sixty-six elapsed days, but do not silently replace one with a constant three hundred sixty-five.
Now decide whether both endpoint dates count as days employed. End minus start counts the elapsed boundaries. If January first, twenty twenty-one itself also counts as an employed date, add one: the inclusive range touches three hundred sixty-seven dates. The convention, not the arithmetic, changed.
Working days are another question. For the same twenty twenty interval, a simple Monday-through-Friday count gives two hundred sixty-two weekdays, before any holiday exclusions. A real employment policy may treat holidays, leave, or part days differently. If the job is ongoing, today's date is a moving endpoint.
For any employment interval, put the dates in order and subtract start from end for elapsed calendar days. Use anniversaries to express calendar years and months, and state whether the last date, weekends, or holidays count. January first, twenty twenty to January first, twenty twenty-one is one calendar year or three hundred sixty-six elapsed days.
Sources
- calculator.academy — Employment duration calculator
- docs.python.org — Datetime.html
- aa.usno.navy.mil — C15 usb online.pdf