What is the day of year?

The day of year (or ordinal day) numbers every day from 1 on 1 January up to 365, or 366 in a leap year, on 31 December. It is sometimes loosely called the Julian day in agriculture, manufacturing and IT.

How is the ISO week number defined?

ISO 8601 weeks start on Monday, and week 1 is the week containing the year's first Thursday. This tool computes the ISO week number for the selected date using that standard.

How many days are in a leap year?

A leap year has 366 days, so 31 December is day 366 instead of 365. A year is a leap year if it is divisible by 4, except century years, which must also be divisible by 400 — so 2000 was a leap year but 1900 was not.

What is the day number for 1 March?

In a common (non-leap) year, 1 March is day 60: 31 days in January plus 28 in February plus 1. In a leap year it is day 61, because February has 29 days. The tool accounts for leap years automatically.

Is the ordinal day the same as the Julian date?

Loosely, yes — many industries call the ordinal day number a 'Julian date', for example in manufacturing lot codes. Strictly, the astronomical Julian Date is a continuous day count since 4713 BC, which is different; this tool gives the ordinal day within the calendar year.

How do I read days remaining in the year?

Days remaining is the year's total days minus the ordinal day. For day 100 of a 365-day year, 265 days remain. It is useful for countdowns and for tracking how far through the year a deadline falls.

Is my date uploaded anywhere?

No. The calculation runs entirely in your browser using local date arithmetic — nothing is sent to a server.

Day of Year Calculator

What day of the year is it?

The day of year (or ordinal day) numbers each day from 1 on 1 January to 365 — or 366 in a leap year — on 31 December. It is widely used in manufacturing date codes, agriculture, logistics and IT systems, where it is sometimes loosely called the “Julian day”. This calculator returns the day number, days remaining and ISO week for any date.

How it works

For the date you pick, the tool counts the whole days from 1 January of that year and adds 1, so 1 January is day 1. It checks whether the year is a leap year (divisible by 4, but century years must be divisible by 400) to set the total at 365 or 366 days, then:

Days remaining = total days − day of year
ISO 8601 week number = the week containing the year’s first Thursday is week 1, with weeks running Monday to Sunday

All arithmetic uses UTC so the result never shifts across time zones.

Example

For 10 April 2026 (a common year):

Day of year: 31 (Jan) + 28 (Feb) + 31 (Mar) + 10 = day 100 of 365
Days remaining: 365 − 100 = 265
ISO week: week 15

Date	Day of year	Days remaining	ISO week
2026-01-01	1 of 365	364	1
2026-04-10	100 of 365	265	15
2024-12-31	366 of 366	0	1 (next year)

Everything is computed locally in your browser — nothing is sent to a server.