Time To Percent Using PHP - php

Question

This may sound like a dumb question, but how can I convert the time between two dates to a percent?
I am using this Jquery plugin: http://tinacious.github.io/goalProgress/
The script on page that calculates the percent is:
$('#timerGoal').goalProgress({
goalAmount: 100,
currentAmount: 40,
textBefore: '',
textAfter: '% Completed.'
});
Where it says goalAmount: I'd like that to remain at 100, but where it says currentAmount: 40, I'd somehow like to find the difference in percentage between two days, I know I'd have to set a start date, current date, and end date to find a percentage.
I'm certain part of the code would have to be:
$startDate = '01/01/2015 12:00:00';
$currentDate = date('d/M/Y H:i:s');
$endDate = '02/15/2015 12:00:00';
Finding the difference in two dates is fairly easy, but it's the third date thing I cannot grasp, especially to make it a percentage.
Any ideas?
I was thinking something along the lines of:
[Taken from: How to find the difference in days between two dates ]
$daylen = 60*60*24;
$date1 = '2010-03-29';
$date2 = '2009-07-16';
echo (strtotime($date1)-strtotime($date2))/$daylen;
But everything I read on is two dates not three.
Here is what I've come up with.
It's not calculating percentages yet, but it's something to possibly go off of:
$startDate = '08/01/2015 12:00:00';
$currentDate = date('d/M/Y H:i:s');
$endDate = '09/01/2015 12:00:00';
$startDate =str_replace(array(':', '/', ' '), '', $startDate);
$currentDate =str_replace(array(':', '/', ' '), '', $currentDate);
$endDate =str_replace(array(':', '/', ''), ' ', $endDate);
$mainPercent = $endDate - $startDate;
$actualPercent = $endDate - $currentDate;
$displayPercent = $actualPercent/$mainPercent * 100;
echo $displayPercent;
With todays date being 08/07/2015 I am getting 901.2015119993 which is obviously not a percent, but it's a start.
Working Solution:
$startDate = strtotime('08/01/2015 12:00:00');
$currentDate = time(date('d/M/Y H:i:s'));
$endDate = strtotime('09/15/2015 12:00:00');
$dateDivideBy = $endDate - $startDate;
$dateDivide = $currentDate - $startDate;
$divideProduct = $dateDivide / $dateDivideBy;
$datePercent = round($divideProduct * 100);
echo $datePercent;
With this working code and todays date being 08/07/2015 the value of $datePercent is 14.

Answer 1

The difference between two times, by itself, really can't be converted to a percentage. It's just a period of time. In order to figure out what percentage is complete, you would need to know how long the entire goal is supposed to take (an estimated time, I assume.) Then you can figure out the percentage like this:
ElapsedTime / TotalTime * 100
The total time would be End Date - Start Date, and the elapsed time would be now - start date.
Rather than using string functions to manipulate the dates, it would be better to use DateTime functions.
$startDate = '08/01/2015 12:00:00';
$endDate = '09/01/2015 12:00:00';
$startDate = new DateTime($startDate);
$currentDate = new DateTime(); // defaults to now
$endDate = new DateTime($endDate);
$totalTime = $endDate->diff($startDate)->format('%a');
$elapsedTime = $currentDate->diff($startDate)->format('%a');
// diff returns a DateInterval object; calling its format method
// with %a returns the number of days in the interval
$percent = ($elapsedTime / $totalTime) * 100;

Answer 2

I believe this is your desired outcome, where result is the resulting percent difference between start_actual_time and percent_time:
var percent_time= new Date("01/17/2013 11:20");
var start_actual_time = new Date("01/17/2012 11:20");
var end_actual_time = new Date("01/17/2014 11:20");
var range = end_actual_time - start_actual_time;
var diff = end_actual_time - percent_time;
var result = (diff / range)*100;
In this example, start_actual_time and percent_time are 40% different.