Thousand Days: Concept

reference copy: Thousand Days: Concept on github.

Stewart Russell – — 2024-03-26, at age 19999 days …


One’s thousand day(s) celebration occurs every thousand days of a person’s life. They are meant to be a recognition of getting this far, and are celebrated at the person’s own discretion.

Who is this for?

  • Maybe your birthday’s on a day associated with an unpleasant event. Your thousand day will never coincide with your birthday.
  • Maybe your birthday’s in the middle of winter, or in another part of the year that you’re not keen on. Your thousand day is every 2 years and 3 seasons, so it shifts back by a season every time it happens.

Quantities and scale

1000 days is approximately:

  • 2.738 years
  • 2 years 269 days
  • 2 years 8.85 months
  • 2 years, 3 seasons.

4000 days is just shy of 11 years.


Compared to regular birthdays, thousand days:

  • must be calculated; they’re not intuitive when they’re going to happen. But we have computers and calendar reminders for that …
  • can be used to work out your actual date of birth, if someone knows that you’re going to be x000 days old on a particular day. It’s possible to know someone’s birthday, but not know their age.



My ancient Your 1000 Day Birthday Calculator, first published in 2002 and untouched since 2010.


So it turns out that GNU date can handle arbitrary date maths quite well. For example:

date --iso-8601=date --date="1996-11-09 + 10000 days"

returns 2024-03-27.

Other Ways

Excel or any other spreadsheet will do, too. Although not for too many years back

People with the same thousand day as you

This is an idea for finding people who have a thousand day on the same day as you. I suggest using 1851-10-01 as a datum, because:

  • nothing particularly interesting happened that day;
  • it’s conveniently 43000 days before my birthday.

then calculate

( (birth_date - 1851-10-01) mod 1000 ) + 1

This results in a number 1 – 1000. Everyone with the same number shares a 1000 day birthday with you.

Why not 0 – 999?

  1. No-one deserves to be a zero;
  2. Wouldn’t be much of a thousand day if it only went up to 999, would it?

Incomplete list of people with day = 1

There are more, but these were found from Wikipedia’s year pages


🅭 2024, Stewart Russell,

This work is licensed under CC BY-SA 4.0.

There are no trademarks, patents, official websites, social media or official anythings attached to this concept. Please take the idea and do good with it.

So why aren’t you implementing this further?

I’ve had this idea kicking around my head for at least the last 20 years. For $REASONS, it turns out I’m not very good at implementing stuff. I’d far rather someone else took this idea and ran with it than let it sit undeveloped.

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