How many days old am I?
This age-in-days quiz answers “How many days old am I?” for your own birthday, but it makes you guess first: how many days you have lived, the year you turn 10,000 days and a billion seconds old, the weekday you were born on, and how far Earth has carried you around the Sun. Each exact answer appears straight after your guess, counted on the calendar from today’s date.
You set your birthday on three wheels and your life unrolls as a party streamer, one loop for each year. Then come five rounds, easy to hard: the day of the week you were born on, how many days old you are today (within 5% counts), the year you turn 10,000 days old, the year you turn a billion seconds old (both exact), and how far you have travelled around the Sun (within 25%). After each guess a flag goes up where your answer lands on the streamer, next to the true one. The score is how many of the five you got: there is no crowd to rank you against, just you and the calendar.
It is arithmetic about time, not a horoscope or a health check: the numbers say nothing about who you are or how long you will live. Ages in days ignore the hour you were born, so a milestone can land a day either side for someone born near midnight, and everything follows the date on your device.
What the quiz asks
One thing: how well you can feel the scale of your own life so far.
The task
- Set your date of birth on three big wheels: year, month and day. It never leaves your device
- Round 1: the day of the week you were born on, one of seven, exact
- Round 2: how many days old you are today, within 5%
- Round 3: the year you turn (or turned) 10,000 days old, exact
- Round 4: the year you turn (or turned) one billion seconds old, exact
- Round 5: how far Earth has carried you around the Sun since you were born, within 25%
- Tap a weekday, or slide and nudge a dial for the others; on a keyboard, arrow keys move and Enter locks it in
Your result
- A score out of 5 and a one-line birthday certificate
- Each guess next to the true value, and how far off it was
- Your coming milestones with their dates: day 10,000, 20,000 and 30,000, second 1, 2 and 3 billion, the next round thousand of days, the next all-one-digit day count such as 11,111, and your next birthday
- Your life so far in days, weeks, trips around the Sun, kilometres, full moons and 29 Februaries
- Where your birth date ranks out of 366 among US births from 1994 to 2014, and how your birth weekday compares
- A share card that shows only the score, and a challenge link that carries no date
Before you start
- About two minutes, five rounds
- Works on a phone or a computer; it needs a browser with 3D graphics (WebGL) switched on
- Sound effects are optional and can be switched off
- Your birthday is not stored or sent anywhere
Age in days: common questions
Is this test free? Do I need to sign up to see my result?
Yes, it’s free, and there’s nothing to sign up for: no account, no email, no payment. Your result appears on this page the moment you finish, and you can share it or play again straight away.
How many days old am I?
Enter your birthday and guess first: the exact count appears the moment you lock in your guess. The count is today’s date on your device minus your date of birth, on the Gregorian calendar with every 29 February included, and the day you were born is day 0. A guess within 5% wins the round, and the result sheet adds your life in weeks, full moons and trips around the Sun.
When will I be 10,000 days old?
The quiz asks you to guess the year first, then shows the exact date: your birthday plus 10,000 days, counted on the calendar. The result sheet goes on to list your day 20,000 and 30,000, the next round thousand of days and the next all-one-digit day count, such as 11,111, each with its date, so you can put them in your calendar.
How old am I in seconds, and when do I turn a billion?
The quiz asks you to guess the year you turn a billion seconds old, then shows the exact date: your birthday plus 1,000,000,000 seconds, at 86,400 seconds a day. The result sheet also gives your second 2 billion and 3 billion. Ages here ignore the hour you were born, so for someone born late in the day the milestone can land a day later.
How far have I travelled around the Sun?
That is the quiz’s last and hardest round, so it asks for your guess first, and within 25% counts as right. The exact distance follows straight after, worked out from your exact number of days and Earth’s mean orbital speed in NASA’s Earth Fact Sheet. The result sheet also gives your life so far in kilometres, trips around the Sun and full moons.
Which day of the week was I born on?
The quiz asks you to guess before it shows you: tap one of the seven days, and your true birth weekday appears straight after. The result sheet then compares your weekday and your birth date with US births from 1994 to 2014, and explains why some days of the week see more births than others.
Is my birthday stored?
No. Everything is worked out in your browser. The share card shows only your score, and a challenge link carries only which of the five rounds you got right and the name you type, never your date of birth.
Where the numbers come from
Days, dates and seconds are plain calendar arithmetic. Distance and full moons use NASA’s published constants. The birth-date rank and weekday figures are our tabulation of the public FiveThirtyEight births data, each date compared with the same weekday in the same year. The site does not publish its own players’ data.
How the numbers are worked out
Days old
Today’s date on your device minus your date of birth, counted on the Gregorian calendar. The day you were born is day 0.
Day 10,000 and second 1,000,000,000
Your birthday plus 10,000 days, and your birthday plus 1,000,000,000 seconds at 86,400 seconds a day, both counted on the calendar. The result sheet turns each into a date.
Distance around the Sun
Days lived × 86,400 seconds × Earth’s mean orbital speed from NASA’s Earth Fact Sheet. The result sheet gives the speed and what it adds up to in a year.
Full moons
Days lived ÷ 29.53, the average time from one full moon to the next in NASA’s Moon Fact Sheet, rounded down.
Scoring
One point a round: the exact weekday, days within 5%, the exact year for day 10,000 and for second 1,000,000,000, and the distance within 25%.