📅 Date Calculator — Add Days, Date Diff & Age
Add or subtract days from any date, calculate the difference between two dates, and compute age from a birthdate. Three calculators in one free online date tool.
How to Use
1
Choose a calculator tab
Select Add/Subtract to offset a date, Date Difference to find the gap between two dates, or Age to compute exact age from a birthdate.
2
Enter your dates
Use the native date picker or type in YYYY-MM-DD format. All calculations update instantly as you change the inputs.
3
Read the result
Results show in multiple units simultaneously — days, weeks, months, and years — so you can use whichever suits your needs.
Frequently Asked Questions
How do I calculate days between two dates?
Switch to the Date Difference tab, enter a start and end date, and the result shows instantly in days, weeks, months, and years.
Can I add business days instead of calendar days?
The current version uses calendar days. A business-days option (skipping weekends and holidays) is planned for a future update.
How accurate is the age calculator?
Very accurate — it accounts for leap years and calculates your exact age in years, months, and days as of today.
What date range does it support?
Any date from the year 0001 to 9999. The native browser date picker handles input validation.
完整指南：日期计算器
这个工具能做什么？
三合一计算器：对任意日期加减天数、计算两个日期间的精确差值（天/周/月/年），以及根据出生日期计算年龄。自动处理闰年和月份长度变化等边缘情况。
如何使用
- 选择标签页：加减天数、日期差或年龄。
- 输入日期。
- 结果以多种格式即时显示。
专业技巧
- 项目截止日期考虑使用工作日而非自然日。
- 以月数表示的差值适合计算订阅和合同期限。
- 代码中使用date-fns或Day.js而非手动操作JS的Date对象。