How is the date difference calculated — is it exact?

Yes. The calculator computes the exact difference using your local timezone. It correctly handles leap years, varying month lengths, and daylight saving time transitions. The total days figure is always precise; the years/months breakdown follows calendar logic (e.g., Feb 1 to Mar 1 is exactly 1 month regardless of how many days February has).

What is the difference between 'Total Days' and the days in the breakdown?

The breakdown shows the remaining days after extracting full years, months, and weeks. For example, a span of 1 year, 2 months, and 5 days shows '5' in the days cell. 'Total Days' is the raw calendar day count from start to end — useful when you need a flat number for payroll, contracts, or scheduling.

Can I calculate a date difference across different years?

Yes, there is no limit on how far apart the dates can be. You can calculate the difference between dates centuries apart for historical research, or just days apart for short-term planning. The tool handles all cases including cross-year, cross-decade, and cross-century spans.

What happens if I set the end date before the start date?

The calculator shows the absolute difference regardless of which date comes first. A note is displayed indicating the dates are in reverse order, but the calculations remain accurate. You can also use the 'Swap Dates' button to reverse them instantly.

Is the date calculation done in my browser or sent to a server?

Everything is calculated locally in your browser using JavaScript's Date API. No data is ever sent to a server. This also means the tool works offline once the page has loaded.

日付差分計算機

2つの日付の正確な差分を年、月、週、日、時間、分、秒で計算します。

開始日

終了日

両方の日付を選択すると差分が表示されます。

使い方

2つの日付の正確な差分を年、月、週、日、時間、分、秒で計算します。

1Enter your start date in the first input field. You can type directly in YYYY-MM-DD format or use the date picker.
2Enter your end date in the second input field. The end date defaults to today so you can quickly calculate how long ago something happened.
3The difference is calculated instantly — the top banner shows a human-readable summary like '2 years, 3 months, 15 days'.
4The grid below breaks down the difference into years, months, weeks, and remaining days for a complete picture.
5Scroll to the totals section to see total days, total weeks, total hours, and total minutes — useful for contracts, payroll, or project tracking.
6If you need to reverse the dates, click the 'Swap Dates' button instead of re-entering them.

主な機能

Multi-unit breakdown — years, months, weeks, and days shown simultaneously for a complete picture
Total counts — flat totals for days, weeks, hours, and minutes ideal for contracts and scheduling
Swap dates — one-click reversal without re-entering anything
Leap year and DST aware — handles edge cases like February 29 and daylight saving transitions
100% browser-based — no server, no uploads, works offline after page load

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Date Difference Calculator — How to Count Days, Weeks, and Months Between Dates