Calculate time difference between 2 date()'s - php

Question

I've got an input field where I type in a deadline in words. For example, "5 minutes", "2 days", "6 weeks", "8 months". What I want for the program to do is to calculate how long it will take when that deadline ends. And also if that deadline is almost ending, for example if 80% of the given time has passed.
I was thinking something like that php splits the given time in seconds, and then checks how many minutes and hours or days fit in those seconds and then puts that in dateTime. Like current date + input = futureDate.
I know I probably shouldn't use percentages, it's just an example.
<input type="text" name="getFutureTime">
<?php
$futureTime = $_POST['getFutureTime'];
$dateNow = date('d-m-Y H:i:s');
if($futureTime > $dateNow){
//Calculate
echo "Deadline has passed";
}else if (($futureTime / 100 * 80) < $dateNow){
//Calculate
echo "Deadline is almost passed";
}
?>

Answer 1

Here the values are string and you cant compare this like that. Convert them to timestamp first. Try with -
$futureTime = strtotime($_POST['getFutureTime']);
$dateNow = time();

Answer 2

I have a solution with, caculate how date later :)..., copy this to localhost and run :) diff
$d1=new DateTime("now");
$d2=new DateTime($_POST['DateInput']);
$diff = $d1->diff($d2);
echo "<pre>";
print_r($diff);
echo "</pre>";
$date = $diff->format('%d'); //It date
$year = $diff->format('%y'); //It year
$month = $diff->format('%m'); //It month
echo $diff->format('%a'). "<br/>";
foreach($diff as $key => $value){
echo $key . "<br/>";
echo $value;
}
$value = strtotime('14/12/2012');
echo($value);
Update
$diff->format('%a') // Is date from now example 10/12/2015 - 10/5/2015 = 7
$diff->format('%a') is 7

Answer 3

Try this it will work:
$date_a = new DateTime('2015-05-07 13:03:48');
$date_b = new DateTime('2015-02-04 13:03:41');
$interval = date_diff($date_a,$date_b);
echo $interval->format('%m Months %d Days %h Hours %i Minutes %s Seconds');