What day of the year is January 1?

January 1 is Day 1 of the year in all years.

What day of the year is December 31?

December 31 is Day 365 in a non-leap year and Day 366 in a leap year.

How do I calculate the day of the year manually?

Sum the days in all complete months before the target month, add any leap-year correction (+1 if the date is after February in a leap year), then add the day of the month. January has 31, February has 28/29, March has 31, April has 30, etc.

What is the ISO ordinal date format?

ISO 8601 ordinal date format is YYYY-DDD, where DDD is the three-digit day of the year with leading zeros. For example, March 1, 2024 = 2024-061.

What is a Julian Date?

A Julian Date is a continuous day count from noon on January 1, 4713 BCE. It is used in astronomy to simplify time-interval calculations across historical epochs without calendar system complications.

What is Modified Julian Date (MJD)?

MJD = JD - 2,400,000.5, which shifts the epoch to November 17, 1858 at midnight. It strips the large leading number from Julian Dates to make them more convenient for modern scientific computing.

What is day 256 of the year?

Day 256 (September 13 in non-leap years or September 12 in leap years) is celebrated by programmers as "Programmers' Day," since 256 = 2⁸ is the number of values representable by one byte.

How many days are in a leap year?

366 days. A leap year adds February 29 (Leap Day) to the calendar, accounting for the approximately 0.2422 extra solar days per calendar year.

What is the day number for February 29?

February 29 is Day 60 in a leap year. It only exists in leap years. In non-leap years, March 1 is Day 60.

How are ordinal dates useful in logistics?

Ordinal dates simplify duration calculations. To find how many days between two delivery dates, simply subtract their ordinal day numbers — no need to count across months or check month lengths.

What is the Gregorian calendar?

The Gregorian calendar, introduced by Pope Gregory XIII in 1582, is the most widely used civil calendar today. It improved upon the Julian calendar by refining the leap year rule to keep the calendar aligned with the solar year over centuries.

J2000.0 is the standard astronomical epoch defined as January 1.5, 2000 (noon on January 1, 2000 UTC), corresponding to Julian Date 2,451,545.0. It is the reference point for many modern astronomical coordinate systems.

utility calculator

Day of the Year & Julian Date Calculator

Find the ordinal day number for any calendar date, compute Julian Date (JD), calculate remaining days in the year, and check if it is a leap year.

Formula Verified by Dr. Arthur Pendelton, PhD

Inputs

Date Selector

Date

Year Progress Gauge

181 of 365 days completed

Results

Ordinal Date Format

2026-181

Day of Year

181

Remaining Days184

Julian Date Number (JD)2461221.5000

Leap YearNo

Formula

Gregorian to Ordinal Date formulas

DayOfYear = Date - Jan1 + 1
YearPercent = (DayOfYear / TotalDays) × 100
Julian Date (JD) = C + D + E + F - 1524.5

Ordinal date is the number of days since January 1. Julian Date represents the continuous count of days since January 1, 4713 BCE.

Step by step

How the calculation works

1Enter any calendar date in the date input.
2Review the day number (1 to 365/366) and remaining year days.
3Check the astronomical Julian Date number calculated.
4Observe the visual percentage completion chart below.

Example

Example Ordinal Calendar Dates

For the date March 1, 2024 (a leap year), the ordinal day number is 61 (31 in Jan + 29 in Feb + 1), leaving 305 days remaining.

Related guides

Learn more about this calculation

Guide

Date Arithmetic Guide: Differences, Deadlines, and Calendar Math

Learn how date arithmetic works, how the DTC date calculator measures elapsed days, and why calendar intervals, deadlines, and age-style borrowing need clear rules.

Site Guide

How to Use Do The Calculation Calculators: A Practical Step-by-Step Guide

Learn the fastest reliable workflow for using Do The Calculation calculators, reading results, checking formulas, and using save, print, share, and export actions correctly.

utility calculator

Day of the Year & Julian Date Calculator

Find the ordinal day number for any calendar date, compute Julian Date (JD), calculate remaining days in the year, and check if it is a leap year.

Formula Verified by Dr. Arthur Pendelton, PhD

Inputs

Date Selector

Date

Year Progress Gauge

181 of 365 days completed

Results

Ordinal Date Format

2026-181

Day of Year

181

Remaining Days184

Julian Date Number (JD)2461221.5000

Leap YearNo

Summary

Key output metrics

Ordinal Day Number

181

Out of 365.

Year Completed

49.6%

Current progress.

Remaining Days

184 days

Left in the year.

D3 visualization

Year Division

Visualize the elapsed days versus remaining days in the calendar year.

Days Elapsed181

Days Remaining184

Formula

Gregorian to Ordinal Date formulas

DayOfYear = Date - Jan1 + 1
YearPercent = (DayOfYear / TotalDays) × 100
Julian Date (JD) = C + D + E + F - 1524.5

Ordinal date is the number of days since January 1. Julian Date represents the continuous count of days since January 1, 4713 BCE.

Step by step

How the calculation works

1Enter any calendar date in the date input.
2Review the day number (1 to 365/366) and remaining year days.
3Check the astronomical Julian Date number calculated.
4Observe the visual percentage completion chart below.

Example

Example Ordinal Calendar Dates

For the date March 1, 2024 (a leap year), the ordinal day number is 61 (31 in Jan + 29 in Feb + 1), leaving 305 days remaining.

Related guides

Learn more about this calculation

Guide

Date Arithmetic Guide: Differences, Deadlines, and Calendar Math

Learn how date arithmetic works, how the DTC date calculator measures elapsed days, and why calendar intervals, deadlines, and age-style borrowing need clear rules.

Site Guide

How to Use Do The Calculation Calculators: A Practical Step-by-Step Guide

Learn the fastest reliable workflow for using Do The Calculation calculators, reading results, checking formulas, and using save, print, share, and export actions correctly.