- What day of the year is it today?
- The Date box opens on your own local date, so the number on screen when the page loads is today's. Counting starts at 1 on January 1, so the day number is the date's position in the year, not the number of days that have passed. September 20, 2026 is day 263 — there are 262 completed days behind it and 102 still to come.
- Is a Julian date the same as the day of the year?
- Two different things share the name, and this catches people out. In manufacturing, food packaging, pharmacy and on mainframes, a "Julian date" is the day of the year, usually written as five digits: two for the year and three zero-padded for the day. 26263 means day 263 of 2026. That's the format this tool outputs. In astronomy, the Julian Day is a continuous count of days since 4713 BC — today's is about 2.46 million. If the number you're reading came off a package or a green-screen terminal, you want the first one.
- Why does a lot code use YYDDD instead of a real date?
- It fits. Five digits sort correctly as text, never need a separator, and survive being stamped, laser-etched, or printed on a curved surface at 6 point. They also sidestep the international argument about whether 03/04 is March 4 or April 3. The cost is that a human can't read one at a glance, which is why an egg carton stamped 26095 needs a lookup to become April 5, 2026. Paste the digits into the Day number and Date boxes here and you have it.
- How do leap years change the day number?
- Only after February. January 31 is day 31 in every year. From March 1 onward a leap year runs one higher: March 1 is day 60 in 2026 and day 61 in 2024, and the whole rest of the year keeps that offset, so December 31 is day 365 in one and day 366 in the other. This is the single most common bug in hand-rolled day-of-year code — a formula that assumes 365 is right three years out of four and quietly wrong in the fourth. The reverse direction shifts too: day 100 is April 10 in 2026 and April 9 in 2024.
- What date is day 100 of the year?
- April 10 in a common year, April 9 in a leap year. Type 100 into the Day number box and the Date box rewrites itself using the year already showing — no separate year picker, no mode to switch. The same works for any number from 1 to 365, or to 366 in a leap year. Ask for day 366 in a year that doesn't have one and the tool says so instead of silently rolling into January.
- Why is the ISO week number not just the day number divided by 7?
- Because ISO 8601 weeks run Monday to Sunday and week 1 is the week containing the first Thursday of January — so a week can start in the previous calendar year. December 31, 2024 is day 366 of 2024 but sits in week 1 of 2025. Dividing 263 by 7 gives 37.6, which rounds to the wrong answer about a third of the time. The week shown here follows the Thursday rule, which is what European delivery schedules, payroll runs and manufacturing calendars mean by KW or week number.
- How do I calculate the day of the year in a spreadsheet?
- Subtract January 1 from your date and add one: =A1-DATE(YEAR(A1),1,1)+1, then format the result as a plain number rather than a date, which is the step everyone forgets. In Python it's date.timetuple().tm_yday or the %j format code; in SQL it's usually DAYOFYEAR() or EXTRACT(DOY FROM ...). All of them agree with this page. The difference is that none of them are open right now.
- How is the percent of the year elapsed worked out?
- Day number divided by the days in that year. Day 263 of 365 is 72.1 percent, and December 31 always reads 100.0 percent because the day you're standing on counts as complete. A leap year divides by 366 instead, so the same calendar date reads a hair lower. It's a progress bar for the year rather than a precise clock — if you need a count to a specific date, the days until calculator does that.
- Does this work for historical dates?
- It works back to the year 1000, using the proleptic Gregorian calendar — the modern rules extended backwards. Most of Europe didn't adopt those rules until 1582, and Britain and its colonies not until 1752, so a date you read in a document from before then was written under the Julian calendar and may sit ten or more days away from where this tool places it. The page says so when you go back that far. For anything after 1752 in the English-speaking world, the day number here is the one you want.
- Is what I type saved or sent anywhere?
- No. The calculation runs in your browser, and the only thing that leaves the page is the link you copy yourself — which carries the date in the URL so whoever opens it sees the same answer. Nothing is stored, nothing is sent to a server, and closing the tab clears it.
