Index / Time
How Many Days Old Am I
A date of birth in, a day count out, along with the weekday you were born on and the dates the round numbers land on. It counts calendar days, so no clock change or leap year moves the answer.
Date of birth
Only used for the hours and minutes rows, and for
the billion-second date. Left empty it assumes midnight and says
so.
Counting up to
Empty means today, wherever this browser thinks it
is. Fill it in to count to any other date — it works
backwards too.
Days old
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Age
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Born on a
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The same span, counted every way
Round numbers
How the counting is done
Days are calendar days, not 86,400-second blocks. The date of
birth and the date today are each turned into a day number on the
proleptic Gregorian calendar and subtracted. Clock changes, leap years
and time zones cannot move that answer by a day, which they can if you
divide a difference in seconds.
Months are counted by clamping, which is the only convention that works at the end of a month. One month after 31 January is 28 February — 29 February in a leap year — because there is no 31 February. So someone born on 31 January is one month old on 28 February in a common year, and one month and one day old on 1 March. The whole months are counted first, and the days left over are counted from the date those months land on. Every calculator that does this differently disagrees only in that one case, and this page says which one it took.
The average month and the average year are not used anywhere. The “in months” row is whole calendar months plus a remainder in days, not the day count divided by 30.44. Dividing by an average is what makes two calculators disagree by a day.
Hours and minutes assume every day is 24 hours. They are the day count multiplied out, adjusted by the time of birth if you gave one. In a country that changes its clocks, the true number of elapsed hours differs by one or two a year, in whichever direction your government chose. The day count above is unaffected.
A leap-day birthday is shown both ways. 29 February exists in one year in four, so the page gives the next real 29 February and the date you would use in the other three years if you count 1 March. Neither is more correct; different jurisdictions pick different ones.
A billion seconds is 11,574 days and 1,600 seconds, which is a little under 31 years 8 months. It is the one milestone here that needs a time of day, so without one it is worked out from midnight.
Nothing is stored and nothing is sent. The date is put in the address bar so the page can be shared or bookmarked; if that is not what you want, clear the box and the link goes with it.
Months are counted by clamping, which is the only convention that works at the end of a month. One month after 31 January is 28 February — 29 February in a leap year — because there is no 31 February. So someone born on 31 January is one month old on 28 February in a common year, and one month and one day old on 1 March. The whole months are counted first, and the days left over are counted from the date those months land on. Every calculator that does this differently disagrees only in that one case, and this page says which one it took.
The average month and the average year are not used anywhere. The “in months” row is whole calendar months plus a remainder in days, not the day count divided by 30.44. Dividing by an average is what makes two calculators disagree by a day.
Hours and minutes assume every day is 24 hours. They are the day count multiplied out, adjusted by the time of birth if you gave one. In a country that changes its clocks, the true number of elapsed hours differs by one or two a year, in whichever direction your government chose. The day count above is unaffected.
A leap-day birthday is shown both ways. 29 February exists in one year in four, so the page gives the next real 29 February and the date you would use in the other three years if you count 1 March. Neither is more correct; different jurisdictions pick different ones.
A billion seconds is 11,574 days and 1,600 seconds, which is a little under 31 years 8 months. It is the one milestone here that needs a time of day, so without one it is worked out from midnight.
Nothing is stored and nothing is sent. The date is put in the address bar so the page can be shared or bookmarked; if that is not what you want, clear the box and the link goes with it.