Day of Year · ISO Week · Julian Day
Pick a date and get the full set of calendar metadata: day-of-year (1–365/366), ISO 8601 week number (W01–W52/W53 with proper week-year handling — Dec 31 might belong to next year's week 1), ISO weekday (1=Monday, 7=Sunday), quarter, Julian Day Number used in astronomy and historical scholarship, Unix timestamp, leap-year flag, and how far through the year you are as a percentage with progress bar.
Day of year
233 / 365
132 days remaining · Year progress: 63.8%
ISO week
2026-W34
Weekday (Mon=1)
5 (Friday)
Quarter
Q3
Julian day
2461273.50
Unix (s)
1787270400
Leap year
No
Computations use UTC. ISO 8601 week numbering — week 1 always contains the year's first Thursday. Julian Day is astronomical, not Julian calendar.
How to use
- Pick a date or click 'Use today'.
- Read the day-of-year and year progress bar.
- Check ISO week, quarter, Julian day for whatever you need (scheduling, astronomy, historical references).
Frequently asked questions
- Why does Dec 31 sometimes show next year's week 1?
- ISO 8601 defines week 1 as the week containing the first Thursday of the year. So Dec 29 2025 belongs to week 1 of 2026 (its Thursday is Jan 1 2026). The 'week year' field tells you which year the week numbering anchors to.
- Why ISO weekday 1 = Monday?
- ISO 8601 chose Monday as the start of the week. (JavaScript's Date.getDay returns 0 for Sunday — the US convention.) This tool uses ISO numbering: Mon=1, Tue=2, …, Sun=7.
- What's Julian Day?
- A continuous count of days since noon UTC on Jan 1, 4713 BC. It's the standard astronomical time scale because it has no month/year boundaries to mess up calculations. Today's Julian Day is around 2.46 million.
- Leap-year rule?
- Divisible by 4, except divisible by 100, except divisible by 400. So 2000 is leap (÷400), 1900 isn't (÷100 but not ÷400), 2024 is (÷4 not ÷100). Comes from the Gregorian reform of 1582.
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