What is the Days Lived Calculator?
This tool counts the exact number of days between your date of birth and any end date you choose (today by default). It also converts that span into weeks, hours, and approximate years. Because the calculation is based on actual calendar dates, it automatically accounts for leap years — so the count is precise rather than a simple multiplication.
How to use it
Enter your birth year, month, and day in the first row. In the second row, enter the end date you want to count up to (it defaults to the current date). Click calculate and you will see the total days lived along with weeks, hours, and a rough number of years.
The formula explained
The calculator converts both dates to a millisecond timestamp at midnight, subtracts the birth timestamp from the end timestamp, and divides by the number of milliseconds in a day (86,400,000). The result is rounded to the nearest whole day. Years are estimated by dividing days by 365.25, the average year length once leap years are taken into account.
$$\text{Days Lived} = \frac{\text{End Date} - \text{Birth Date}}{86400\ \text{s}} \\[1.5em] \text{where}\quad \left\{ \begin{aligned} \text{End Date} &= (\text{End Year},\ \text{End Month},\ \text{End Day}) \\ \text{Birth Date} &= (\text{Birth Year},\ \text{Birth Month},\ \text{Birth Day}) \end{aligned} \right.$$
Worked example
From January 1, 2000 to January 1, 2020 there are 20 years. Five of those years are leap years (2000, 2004, 2008, 2012, 2016), so the span is
$$15 \times 365 + 5 \times 366 = 5{,}475 + 1{,}830 = 7{,}305 \text{ days}.$$That equals about 1,043.6 weeks, 175,320 hours, and roughly 20 years.
FAQ
Does it count the end date itself? No — it counts the elapsed days between the two dates, so a date compared with itself gives 0 days.
Why use 365.25 for years? A calendar year averages 365.25 days once a leap day is added every four years, giving a more accurate "approximate years" figure than 365.
Can I count to a future date? Yes. Set the end date later than today to count days until a milestone, or earlier to look back.
