Short answer
Weeks between two dates
Calculate full weeks and remaining days without misleading rounding.
Difference
Inputs are calendar dates without a time. ISO classification is therefore independent of the device time zone.
Short answer
The tool first finds the calendar-day difference, then splits it into complete seven-day blocks.
How it works
Input order is preserved, so reverse comparisons return negative values.
Duration is not the number of weeks touched
The duration is end date minus start date in calendar days. The same date gives zero days; 13 days give one full week and six remaining days. Both endpoints are not counted inclusively as extra days.
This is not a working-day calculation. Weekends and public holidays do not reduce the result. Reversing the dates gives a negative duration. Date-only arithmetic counts calendar days across daylight-saving changes; it does not measure elapsed hours between time-stamped instants.