What Is the 100th Day of the Year? April 10, or April 9 in Leap Years

The 100th day of the year is April 10 in a common year and April 9 in a leap year. The rule comes from the leap-year definition of the U.S. Naval Observatory (USNO), which adds February 29 to years “evenly divisible by 4,” with exceptions for century years. The table further down lists day 100, day 200 and day 300, with weekdays, for every year from 2024 to 2040, and a one-page printable carries the same list.

100th day of the year: April 10 or April 9

Add up the first three months and you land 90 days in, or 91 when February has 29 days. Day 100 is therefore the 10th of April in a common year and the 9th in a leap year. It cannot fall on any other date, so the answer to “is it always in April” is yes.

Year type	January	February	March	Days through March 31	Day 100
Common (365 days)	31	28	31	90	April 10
Leap (366 days)	31	29	31	91	April 9

The USNO says 1700, 1800, 1900 and 2100 are not leap years, while 1600, 2000 and 2400 are. Every year in this story’s table follows the plain divisible-by-4 rule, and 2024, 2028, 2032, 2036 and 2040 are the leap years.

How to count to day 100 yourself

Use this order for any year.

1. Decide whether the year is a leap year. If it divides evenly by 4 (and is not a century year that fails the USNO test), February has 29 days.
2. Add January, February and March: 90 days, or 91 in a leap year.
3. Subtract that total from 100. The result is the day of April: 10, or 9.
4. For a weekday, look the date up on a calendar, such as our printable yearly calendar, or use the table below.

A spreadsheet does the same count with its date function (DATE). In Google Sheets, =DATE(2027,1,100) returns April 10, 2027, because Google’s help page says the function “will silently recalculate numeric dates which fall outside of valid month or day ranges.” Our guide to calculating the day of the year covers the reverse step, from a date to its number. To see how many days are still ahead of any date, read how many days are left in the year.

Day 100, 200 and 300 for every year from 2024 to 2040

We computed each date twice, once with JavaScript’s date functions and once with a Julian-day-number formula, and kept only the rows where both agreed. Day 200 is July 19 (July 18 in a leap year) and day 300 is October 27 (October 26 in a leap year).

Year	Type	Day 100	Day 200	Day 300
2024	Leap	Tue., April 9	Thu., July 18	Sat., Oct. 26
2025	Common	Thu., April 10	Sat., July 19	Mon., Oct. 27
2026	Common	Fri., April 10	Sun., July 19	Tue., Oct. 27
2027	Common	Sat., April 10	Mon., July 19	Wed., Oct. 27
2028	Leap	Sun., April 9	Tue., July 18	Thu., Oct. 26
2029	Common	Tue., April 10	Thu., July 19	Sat., Oct. 27
2030	Common	Wed., April 10	Fri., July 19	Sun., Oct. 27
2031	Common	Thu., April 10	Sat., July 19	Mon., Oct. 27
2032	Leap	Fri., April 9	Sun., July 18	Tue., Oct. 26
2033	Common	Sun., April 10	Tue., July 19	Thu., Oct. 27
2034	Common	Mon., April 10	Wed., July 19	Fri., Oct. 27
2035	Common	Tue., April 10	Thu., July 19	Sat., Oct. 27
2036	Leap	Wed., April 9	Fri., July 18	Sun., Oct. 26
2037	Common	Fri., April 10	Sun., July 19	Tue., Oct. 27
2038	Common	Sat., April 10	Mon., July 19	Wed., Oct. 27
2039	Common	Sun., April 10	Tue., July 19	Thu., Oct. 27
2040	Leap	Mon., April 9	Wed., July 18	Fri., Oct. 26

Day 100 of 2027 is Saturday, April 10. In 2028, a leap year, February adds a day, so day 100 is Sunday, April 9.

How is day 100 written as an ordinal date?

An ordinal date gives the year and the day number instead of a month and day. A summary of the International Organization for Standardization (ISO) 8601 date standard, hosted by NASA, shows the form “1995-035” and says day numbers run from 001 to 365 (366 in leap years). Day 100 of 2027 is written 2027-100, and day 100 of 2028 is 2028-100, even though the first falls on April 10 and the second on April 9. Our guide to the Julian date calendar for 2027 and 2026 offers printable day-of-year charts for both years. Browse the April printable calendars to see where the 9th and 10th sit in the month.

Is the 100th day of school the same count?

No. Schools count the 100th day of school in school days, so it lands on a different date in each district. It has no link to the ordinal day-of-year count above.

Print the day 100 list

The printable on this page puts the table on one US Letter sheet, with an ink-saver version for home printers. It has day 100, day 200 and day 300 for each year from 2024 to 2040.