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Julian Day Calculator

Date: 05/18/2003 at 10:20:51
From: Tom
Subject: Calculating elapsed number of days

What is the equation for calculating the elapsed number of days? For 
example, if I want to know my exact age in days without counting out 
the days, what would be the equation?


Date: 05/18/2003 at 10:32:18
From: Doctor Jerry
Subject: Re: Calculating elapsed number of days

Hi Tom,

Thanks for writing to Ask Dr Math.

Suppose you were born in 1991, say on June 1.

So, you have the number of days in 1991 plus the days in 1992, 1993, 
..., 2002, and then the number of days in 2003 up until today (May 
18).

We have to remember leap years.

1991: not a leap year; add up the days for June, July,...,December; 
this would be 30+31+31+30+31+30+31.

1992: leap year; 366 days

and so on.

2003: not a leap year; add up January,...,April, and then part of May.

There's an entirely different way, but it's somewhat more difficult.  
You can look up the idea of Julian Day in astronomy. Any date can be 
given a Julian Day. So, all you have to do is to look up the Julian 
Day numbers for your birth date and today's date and subtract. Then 
you would need to add 1. (You need to add one because if the Julian 
Days were 7,8,9,10, and 11, then there are five days, but 11-7=4.

Here's a Web page for a Julian Day calculator.

   JD Calculator - Walter MacDonald
   http://www.starlightccd.com/walter/bytebook/javascript/jdcalc.htm 

- Doctor Jerry, The Math Forum
  http://mathforum.org/dr.math/ 
Associated Topics:
Elementary Calendars/Dates/Time
Middle School Calendars/Dates/Time

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