日期差计算、倒计时、年龄及时间持续计算工具。
当您需要按公历精确计算天数、以多种单位表示年龄或衡量经过时间时使用本分类——不适合用心算代替。D-Day 与日期间隔工具回答的是不同问题（距单一目标的倒计时 vs 两个日期之间的跨度），混用很常见。年龄工具可能在专门页面适用地区计岁习惯，请务必确认所用规则。结果由您输入的日期唯一确定；除非页面另有说明，否则不包含工作日、节假日或合同条款。
以下逐一说明每个计算器的用途、前提与常见错误。先了解假设，再解读结果。
Find your exact age in years, months, and days — accurate to the day. Enter your date of birth and optionally choose a custom "as of" date to calculate age at any point in time, past or future. Leap years are handled automatically. Includes Korean man-nai (만 나이) for Korean administrative contexts.
The D-Day Calculator counts exactly how many days remain until a future event — or how many days have passed since a past date. The name comes from military usage where "D" marks a designated target date, but in everyday use it is most commonly used for personal and professional countdowns: exam dates, travel departures, product launches, anniversaries, visa expiry dates, payment due dates, and project deadlines. Unlike the Date Difference Calculator (which compares two arbitrary dates you specify), a D-Day calculator is oriented around today — it automatically answers "how many days until or since [event]?" You can also set a custom start date if you need to count from a date other than today.
The Date Difference Calculator answers one deceptively simple question: exactly how far apart are two dates? Enter a start date and an end date to get the precise gap in days, weeks, months, and years. This is most useful when the exact count matters — for project deadlines where contract language specifies "30 calendar days," for lease expiry calculations where one day off has legal consequences, for loan term verification, for checking how long until a visa or passport expires, or for confirming probationary periods and notice periods at work. The month count uses actual calendar months, not 30-day approximations — so the gap from January 1 to March 1 is exactly 2 months regardless of how many days are in January and February. A business days option (excluding weekends) is available for work-related calculations.
The Time Duration Calculator finds the exact duration between any two times of day — down to the second. Enter a start time and end time to get the elapsed time in hours, minutes, and seconds. You can also add a duration to a start time to find the end time, or sum multiple time intervals together for total time tracking. The calculator handles overnight durations (crossing midnight) automatically. Ideal for tracking work sessions, timing events, calculating billing increments, cooking timers, and travel time planning.
在日期差计算器输入开始与结束日期，即可查看总天数、周数和月数。
可以。年龄计算器会显示年、月、日以及自出生以来的总天数。
输入目标日期，即可倒数（或正数）到该日的准确天数。
会。日期工具会自动考虑闰年、各月天数与夏令时转换。