日期计算器指南：如何计算日期差和工作日
Date arithmetic — adding days to a date, finding the span between two dates, or counting business days — is deceptively tricky. Months have different lengths, leap years add a day, and weekends don't count as work days. This guide explains how a date calculator handles all of it.
Counting Days Between Two Dates
The absolute difference is converted into days, then broken into weeks + days for readability.
Example: from January 1, 2026 to August 7, 2026 is 218 days, or 31 weeks and 1 day.
Adding or Subtracting Days
To add N days to a date, the calculator walks forward through the calendar: if the result overshoots the end of a month, it rolls into the next month, accounting for leap years when crossing February.
Adding months is trickier than adding days — "one month after January 31" is ambiguous (Feb 28? Mar 3?). Most calculators cap at the last day of the target month.
Business Days vs. Calendar Days
For project planning you often need working days only — excluding Saturdays and Sundays, and sometimes public holidays. The calculator can count just the weekdays between two dates, giving you a realistic timeline for deliverables.
Why Leap Years Matter
When a date range crosses February 29 in a leap year, the day count is one higher than the same range in a non-leap year. The calculator detects leap years automatically using the rule: divisible by 4, but not by 100 unless also by 400.
Put It Into Practice
Enter two dates to count the days between them, or pick a start date and add/subtract any number of days, weeks, or months.
日期算术——向日期添加天数、查找两个日期之间的跨度（date difference），或计算工作日——看似简单却暗藏玄机。月份长度不同，闰年多出一天，周末不算工作日。本指南将解释日期计算器如何处理所有这些情况。
计算两个日期之间的天数
绝对差值转换为天数后，为便于阅读，会拆分为周数 + 天数。
示例：从 2026 年 1 月 1 日到 2026 年 8 月 7 日为 218 天，即 31 周零 1 天。
添加或减去天数
向日期添加 N 天时，计算器会沿着日历向前推移：如果结果超出当月末尾，则滚动到下个月，并在跨越二月时考虑闰年。
添加月份比添加天数更棘手——"1 月 31 日之后的一个月"是有歧义的（2 月 28 日？3 月 3 日？）。大多数计算器会限定在目标月份的最后一天。
工作日 vs. 日历日
在项目规划中，你通常只需要工作日——排除周六和周日，有时还需要排除公共假期。计算器可以只计算两个日期之间的工作日，为你提供切实可行的交付时间线。
闰年为何重要
当日期范围跨越闰年的 2 月 29 日时，天数计算会比非闰年中相同范围多一天。计算器使用以下规则自动检测闰年：能被 4 整除，但不能被 100 整除，除非也能被 400 整除。
付诸实践
输入两个日期以计算它们之间的天数，或选择一个起始日期并添加/减去任意天数、周数或月数。
Try the Date Calculator
Add/subtract days, count between dates, and exclude weekends.
📅 Open Date Calculator →