Find the Day Number for Any Date Find what day of the year (1-365) any date falls on, with a visual progress bar.

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Day of Year Calculator

Find what day of the year (1-365) any date falls on, with a visual progress bar.

Select a Date

Choose any date using the date picker.

View Day Number

See which day of the year (1-365 or 1-366) the date falls on.

Check Progress

View the year progress bar, days remaining, and ordinal date format.

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What Is Day of Year Calculator?

The Day of Year Calculator tells you which day number (1 through 365 or 366) any given date falls on within its year. It shows a visual progress bar indicating how far through the year the date falls, along with the percentage complete, days remaining, whether the year is a leap year, the day of the week, and the ordinal date format (YYYY-DDD) used in some technical applications. This information is useful for logistics planning, agricultural schedules, astronomical calculations, and any system that uses ordinal dates rather than month-day notation.

Why Use Day of Year Calculator?

Instant day-of-year lookup with visual progress bar
Shows days remaining in the year
Ordinal date format (YYYY-DDD) for technical use
Leap year awareness (365 vs 366 days)
Percentage of year completed
Runs in-browser with no data upload

Common Use Cases

Ordinal Date Systems

Convert calendar dates to ordinal day numbers used in some data systems.

Year Progress Tracking

Visualize how much of the year has passed for goal tracking.

Agricultural Planning

Reference planting and harvest schedules that use day-of-year notation.

Astronomical Calculations

Many astronomical formulas use the day of year as an input parameter.

Data Analysis

Convert dates to day-of-year for seasonal pattern analysis in datasets.

Technical Guide

The day of year is calculated as the difference in days between the input date and January 0 (December 31 of the previous year) of the same year. This is done by creating a Date object for January 0 and subtracting its timestamp from the input date's timestamp, then dividing by the number of milliseconds in a day (86,400,000). Leap year detection uses the standard rule: divisible by 4 AND (not divisible by 100 OR divisible by 400). The progress bar width is calculated as (dayOfYear / totalDaysInYear) * 100 percent. The ordinal date format concatenates the year with a zero-padded 3-digit day number.

Tips & Best Practices

1
Day 1 is always January 1st, day 365 (or 366) is December 31st
2
The ordinal date format YYYY-DDD is used in some scientific and military contexts
3
Use the progress bar as a motivational "year percentage" tracker
4
In leap years, dates after February 28 are shifted by one day number compared to non-leap years
5
Combine with the Week Number Calculator for complete date context

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Frequently Asked Questions

Q What is the maximum day number?

In regular years the maximum is 365 (December 31). In leap years it's 366.

Q Does it handle leap years?

Yes, the calculator correctly identifies leap years and uses 366 as the total days, shifting all dates after February 28 by one position.

Q What is the ordinal date format used for?

The ordinal date format (YYYY-DDD) is used in some scientific, military, and aviation contexts. It's part of the ISO 8601 standard.

Q Is day-of-year the same as Julian day?

No, the Julian Day Number is a continuous count of days since a reference point in 4713 BCE. Day-of-year counts days within a single year (1-365/366).

Q What is the progress percentage based on?

It's (day of year / total days in year) × 100. On July 2 of a non-leap year, for example, you're about 50% through the year.

About This Tool

Day of Year Calculator is a free online tool by FreeToolkit.ai. All processing happens directly in your browser — your data never leaves your device. No registration or installation required.