random day of the year 1 to 365

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A random day of the year, from 1 to 365

Every date in an ordinary year has a day number, from 1 for January 1 to 365 for December 31. This page is set to that range: press Generate and you get a day of the year, each with a chance of one in 365, about 0.27%.

Turning the number into a date

In a year that is not a leap year, the months end on these day numbers: January 31, February 59, March 90, April 120, May 151, June 181, July 212, August 243, September 273, October 304, November 334 and December 365. Find the first month end that is at least your number, then count back. Day 100 is April 10, for example, and day 256 is September 13. In a leap year, such as 2028, add one to any day after February 28, or set the highest number to 366.

The birthday problem

How many people do you need in a room before two of them probably share a birthday? Half of 365 sounds like a reasonable guess. The real answer is 23: with 23 random birthdays, the chance of at least one shared date is about 50.7%. With 40 people it rises to about 89%. Try it with this page: ask for 20 numbers with No repeats off and look for a duplicate. You will find one surprisingly often.

Uses for a random day

  • Pick the date of a yearly event, a surprise or a challenge.
  • Choose a random day of a diary, a photo archive or a calendar of saints or historical events to read about.
  • Create test data with realistic dates spread across the year.

For a day within one month, use the 1 to 31 page.

Picking several numbers from 1 to 365

365 possible numbers. What changes when you pick more than one at a time:

Numbers pickedA given number is among them (No repeats on)At least one number twice (No repeats off)
10.27%0%
20.55%0.27%
30.82%0.82%
51.4%2.7%
102.7%11.7%
205.5%41.1%

How it works

  1. The range is set

    The lowest and highest numbers for this page are already in the sentence at the top, and both can come up. Nothing to type before your first pick.

  2. Pick your number

    Press Generate or the Space bar, or tap the number. The reel rolls like a slot machine and stops on the result.

  3. Change it if you need to

    Tap how many numbers you want in the sentence to get up to 20 at once; No repeats keeps them all different. Tap either end of the range to type a new one.

Any suggestions for improvement?

We build tools that are as simple and intuitive as possible, with a few bonuses here and there. Tell us what would make this one better.

Ready-made versions

Random numberNumber 1 to 100Number 1 to 10Number 1 to 6Number 1 to 20Number 1 to 50Number 1 to 1000Number 1 to 3Number 1 to 4Number 1 to 5Number 1 to 8Number 1 to 12Number 1 to 15Number 1 to 25Number 1 to 30Number 1 to 31Number 1 to 40Number 1 to 49Number 1 to 52Number 1 to 60Number 1 to 75Number 1 to 90Number 1 to 200Number 1 to 5001 to 10,000

Questions

How many people do you need for a shared birthday to be likely?

Twenty-three. With 23 random birthdays, the chance that at least two match is about 50.7%. This assumes all days are equally likely and ignores February 29.

What date is day 100 of the year?

April 10 in a regular year and April 9 in a leap year.

How do I include February 29?

Tap 365 in the sentence and change it to 366. Day 60 is then February 29, and every later day shifts by one.

Is the random number generator free?

Yes. It is free to use, funded by advertising, with no account and no app to install.

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