Day 100 of the year
The 100th day of 2026 is Friday, April 10, 2026. It was 166 days ago.
Where day 100 lands in other years
The calendar date for a given day number moves only because of leap years. In a common year day 100 is one date; from 1 March in a leap year it shifts back by one.
| Year | Date | Weekday | Leap year |
|---|---|---|---|
| 2026 | April 10 | Friday | no |
| 2027 | April 10 | Saturday | no |
| 2028 | April 9 | Sunday | yes |
| 2029 | April 10 | Tuesday | no |
| 2030 | April 10 | Wednesday | no |
Day 100 in context
Day 100 sits in April, on the 10th of the month, in the second quarter. By that point 99 days of the year have already gone and the year is 27.4% complete.
| Anchor | Day number | Distance from day 100 |
|---|---|---|
| 1 January | 1 | 99 days before |
| 1 April | 91 | 9 days before |
| 1 July | 182 | 82 days after |
| 1 October | 274 | 174 days after |
| 31 December | 365 | 265 days after |
Counting to and from day 100
Ordinal day numbers make in-year arithmetic trivial: the gap between two dates in the same year is just the difference of their day numbers. Day 100 minus today's day 266 gives 166 days, with no month lengths to reason about. That is exactly why batch codes, expiry stamps and flight schedules use them.
Questions
- What date is day 100 of the year?
- Friday, April 10, 2026.
- What weekday is it?
- A Friday in 2026.
- How far away is it?
- 166 days ago.
Reading the number back
To go the other way, from a calendar date to a day number, add up the lengths of the months before it and then add the day of the month. For April 10 in 2026 that is 90 days across the earlier months plus 10, giving 100. The only wrinkle is February, which is why the same date can carry two different day numbers depending on whether the year is a leap year.