When is my billionth second?
By Matthew Parrott, who makes Life Tally ·
You turn a billion seconds old at 31 years and about 8 months. Type your birthday, and the minute you were born if you know it, to see the exact day and time.
Free to download · iPhone and iPad
How the billionth second is counted
A billion seconds is 11,574 days, 1 hour, 46 minutes and 40 seconds. Start the count at the minute you were born, or at midnight on your birthday if you don't know it, and add a billion seconds: that's the moment. It lands in your 32nd year, at 31 years, 8 months and 6 to 10 days old, depending on your birthday.
Unlike your 10,000th day, which is a date, the billionth second is a moment, so the clock time it strikes depends on your time zone. The calculator shows it where you are.
The second your count reads the speed of light
Light travels 299,792,458 metres every second. When your count of seconds reads that exact number, at 9 years, 5 months and 28 days to 9 years, 6 months and 1 day old, you've worn the speed of light once as an age. Life Tally calls it the Lightspeed Second. Two or three days later, the count reads the round 300,000,000.
What Life Tally does on the day
Life Tally dates your billionth second, and everyone else's you add, years ahead. The morning it lands, the app opens with a ceremony, a card to save or send, and the arithmetic: the seconds, the days they make, and the minute they strike.
Checked against Life Tally 4.0 on October 27, 2026.
Questions
How old are you when you're a billion seconds old?
31 years and about 8 months: 31 years, 8 months and 6 to 10 days, depending on your birthday. A billion seconds is 11,574 days, 1 hour, 46 minutes and 40 seconds.
Do I need to know my birth time?
Not for the day, most of the time. A billion seconds is 11,574 days and 1 hour, 46 minutes and 40 seconds, so the billionth second falls 11,574 days after your birth date, unless you were born after 10:13:20 PM, when it rolls over to the next day. Add the minute you were born and the calculator gives the exact clock time too.
What is the Lightspeed Second?
Light travels 299,792,458 metres every second. The Lightspeed Second is the moment your count of seconds reads that exact number, 3,469 days, 19 hours, 40 minutes and 58 seconds after you were born: at about nine and a half years old. Life Tally names it for you and everyone you add.
Does daylight saving time change my billionth second?
Not the moment: a second is a second, and the count runs straight through clock changes. It can change what the clock says by an hour, if daylight saving time was on when you were born and isn't on the day it lands, or the other way round. The calculator reads the clock where you are now.
How many seconds old am I right now?
The age in days calculator shows it, counting live from midnight on the day you were born. Life Tally does the same on its Today screen, from the minute you were born if you add it.