Date & Time

Day of the Year Calculator (Day Number)

Pick a date to see its day number and how much of the year is left.

By TheCalcTools Updated Formula checked and tested

Your numbers

Your results

Day of the year
Day of the year
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Days left in the year
—
Share of the year passed
—
Days in the year
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Ordinal date (YYYY-DDD)
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Day of the Year Calculator (Day Number) by TheCalcTools

How the Day of the Year Calculator (Day Number) works

The day of the year counts from 1 on 1 January. In leap years, 31 December is day 366. The ordinal date form YYYY-DDD is used in logistics, manufacturing lot codes and science.

Days left counts the days after the chosen date up to and including 31 December.

The formula

Day number = date − 1 January + 1

Worked example

Using the default values shown in the calculator:

Date2026-10-17
  1. 17 October 2026 is day 290 of 365, so 75 days remain (79.5% of the year has passed).

Result:

Day of the year290
Days left in the year75
Share of the year passed79.5%
Days in the year365
Ordinal date (YYYY-DDD)2026-290

Frequently asked questions

What day of the year is it today?

Open the calculator: the date defaults to today.

Sources and further reading

Week Number Calculator (ISO 8601)Find which week of the year a date falls in, or the start and end of any week number Day of the Week Calculator (What Day Was It?)Pick any date to see which day of the week it falls on Leap Year CalculatorEnter a year to see if it is a leap year and when the next one is Countdown Calculator (Days Until a Date)Pick an event date to see exactly how long is left Birthday Calculator (Next Birthday and Countdown)Enter your date of birth to count down to your next birthday Add Business Days Calculator (Date After N Working Days)Enter a start date and a number of working days to find the due date

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This calculator gives estimates for information only. Check important results independently before you rely on them. See our disclaimer.