Age milestones worth celebrating

Birthdays are lovely, but they’re not the only way to mark time. Count your age in days, weeks or seconds and new milestones appear, often at unexpected moments. Here are the best ones, and how to find yours.

Milestones by the numbers

These milestones fall at the ages below for someone born on 1 January 2000. For other birth dates the age can differ by a day or two, depending on how many leap days fall in between.

Our age in days calculator shows your own day-count milestones with exact dates, and counts the seconds live.

The 10,000-day birthday

Ten thousand days falls at about 27 years and 4½ months, usually at an age when nobody is planning a party. That’s what makes it fun: it’s a genuine round-number milestone that most people miss. The next ones, at 20,000 and 30,000 days, arrive at about 54¾ and 82 years old.

A billion seconds

A billion seconds is just under 31 years and 8 months. If you know your time of birth, you can pin it down to the hour; enter it in the main age calculator and watch the seconds counter. Two billion seconds arrives at about 63 years and 4 months.

Weeks and months

Counting in weeks gives some memorable markers: 1,000 weeks is just over 19 years old, and 4,000 weeks is about 76½ years, roughly the length of a long human life, which has made it a popular way to think about how to spend time. Counting in months, 500 months is about 41 years and 8 months.

Half birthdays and golden birthdays

• Half birthday: six months after your birthday. Children often celebrate it, and it’s a handy marker if your birthday falls near a holiday. Our birthday countdown shows how far through the year you are.
• Golden birthday: the year you turn the age that matches the day of the month you were born on, such as turning 21 on 21 March. Everyone gets exactly one; for people born on the 1st, it’s their first birthday.

Your age on other planets

A “year” is one trip around the Sun, and every planet takes a different time. Here’s how long a year lasts on some of our neighbours, and how old a 30-year-old Earthling would be there:

Mars is the favourite: a Martian year is about 687 Earth days, so Martian birthdays come round roughly every 22½ months. On Saturn, almost nobody has reached their third birthday.

Planning a milestone celebration

Round-number days and seconds rarely fall on a weekend, so look ahead: the age in days calculator lists your upcoming milestones with their dates, and the birthday countdown shows which weekday your next six birthdays fall on. To understand how these counts are calculated, including leap days, read how to calculate age manually.