All your round numbers in one place
Most of us celebrate one milestone a year, our birthday. But if you count your life in days, weeks, months or seconds, round numbers arrive far more often. You pass a thousand days roughly every two years and nine months, a hundred months every eight years and four months, and a hundred million seconds a little over every three years. Add planet birthdays and the big birthdays that end in zero, and there is something worth noticing every few months. This page collects them all on one timeline.
Use the coloured buttons to show or hide each kind, and the slider to look a few years ahead or decades into the future. Every milestone has a tick box, so you can choose the ones you care about and send them straight to your calendar.
How we calculate it
For days, weeks and seconds we add the round number to your date of birth, following the real calendar so that leap days count. Months are whole calendar months, landing on the same day of the month as your birth, or the last day of shorter months. Planet birthdays divide the time since your birth by each planet’s orbital period from NASA: 686.98 Earth days for Mars and 4,332.59 for Jupiter. Big birthdays are the decade birthdays plus 18 and 21.
| Kind | Step we use | How often |
|---|---|---|
| Days | every 1,000 | about every 2 years 9 months |
| Weeks | every 500 | about every 9 years 7 months |
| Months | every 100 | every 8 years 4 months |
| Seconds | every 100 million | about every 3 years 2 months |
| Mars birthdays | each one | about every 1 year 10 months |
| Jupiter birthdays | each one | about every 11 years 10 months |
Worked example. For someone born on 12 April 1990, the next milestones after 30 October 2026 include their 20th Mars birthday on 23 November 2027, 14,000 days and 2,000 weeks together on 10 August 2028, and 1.2 billion seconds on 20 April 2028.
Why bother with milestones?
Milestones are excuses: to pause, to celebrate, to check in on goals or to do something a bit out of the ordinary. Having a handful of personal dates that nobody else knows about makes the calendar feel more like your own. Pick two or three that appeal to you and put them in your diary now; future you will be pleased you did.
Questions people ask
Which milestones are included?
Round numbers of days (every 1,000), weeks (every 500), months (every 100) and seconds (every 100 million from 500 million), plus planet birthdays on Mars and Jupiter and round-number birthdays such as 30, 40 and 50.
Can I put them in my calendar?
Yes. Tick the ones you like, or leave them all ticked, and the calendar button downloads a file that works with Google Calendar, Apple Calendar and Outlook.
Why do some milestones fall close together?
Different units line up from time to time. For example, 10,000 days and 1.5 billion seconds are years apart, but 2,000 weeks and 14,000 days are the same day, because 2,000 × 7 = 14,000.
How far ahead does it look?
Up to your 100th birthday. Use the range control to show only the next few years if the list feels long.
Sources. Gregorian calendar; NASA planetary orbital periods. Calculations run in your browser; nothing you enter is sent anywhere.