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Date Difference Calculator
Count days between dates, or add / subtract days.
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How the days between two dates are counted
The difference is (end − start) ÷ 1 day, computed on calendar dates (no time of day), so daylight saving changes never cause off-by-one errors. By default the start date is counted and the end date is not — the same convention as "how many nights". Tick Include the end date to count both ends, which is what you usually want for durations such as holidays or contracts.
Business days count Monday to Friday only; public holidays are not subtracted because they differ by country. The breakdown into years, months and days uses whole calendar months.
Adding months to the 31st
When you add months and the target month is shorter, the result is clamped to the last day of that month — for example 31 January + 1 month = 28 (or 29) February. Years, months, weeks and days are applied in that order.