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yutils
Example

Input (between mode)

Start: 1995-06-15
End:   2026-05-13

Output

Exact:   30 years 10 months 28 days
Total days:  11,290
Total weeks: 1,612w 6d
Total hours: 270,960
Total mins:  16,257,600

Note

Four modes: between / add / convert / D-day. The D-day mode adds labeled dates as D-N · D-Day · D+N entries, sorted by proximity — stored in localStorage.

Usage / FAQ

When to use

  • Compute project, contract, or warranty durations
  • Track anniversaries or vacation D-days (persisted in localStorage)
  • Find date + N days = which date (deadlines, …)
  • See how many days since a user signed up (customer success)
  • Accurate duration math that respects leap years and varying month lengths

FAQ

Q.Is every year 365 days?
A.No — leap years have 366. This tool gets it right. Outputs like "30 years 10 months 28 days" follow the actual calendar and can differ from naive `days / 365`.
Q.Why are some D-days negative?
A.Sorted by absolute proximity. A D+5 event (5 days ago) may sit closer to today than a D-30 (30 days away), so they're shown together by closeness in time.
Q.My D-day list disappeared!
A.Stored only in localStorage — clearing browser data, using incognito mode, or moving to another device loses it. Back up important dates in a calendar too.
Fun facts

  • The Julian Day Number was introduced in 1583 by astronomer Joseph Scaliger — a continuous day count with epoch January 1, 4713 BC. He picked a far-enough-back start so that every astronomical and historical event could be compared as a single number. 'Julian' is named for his father, Julius.

    Wikipedia — Julian day

  • When the Gregorian calendar arrived in 1582, Catholic countries skipped from Thursday, October 4, to Friday, October 15 — a 10-day jump to fix accumulated Easter-calculation drift. Britain and the US made the switch in 1752 with an 11-day jump (Sept 2 → Sept 14), and some Orthodox countries kept the Julian calendar into the 20th century.

    Wikipedia — Gregorian calendar

  • The Gregorian leap-year rule is '4, but not 100, except 400' — so 2000 was a leap year while 1900 and 2100 are not. The 365.2425-day average is just 26 seconds off the true tropical year (365.24219), drifting by about a day every 3,000 years.

    Wikipedia — Leap year

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