Unforeseen results occur when calculating time difference in seconds in PHP by converting two dates to Unix timestamps.

Question

As per the title, I am trying to find the difference in seconds and then convert those seconds to days and hours.

After reading and following similar questions, I built a function that adds the hour, day, week, month, or year I want to today's datetime, and I get the correct results from this part.

However, I then tried converting the two dates (start date and move date) to unix timestamps, subtracting both timestamps to find the difference between the two dates in seconds, and then converting I don't get the results I expected for days or minutes (/86400 and /3600).

This is the code..

<?php
$dateTimeNow = date();

function dateTimeShift($dateTimeIn, $lengthNum, $lengthWord) {
$shifted = date("Y-m-d H:i:s", strtotime($dateTimeIn." $lengthNum $lengthWord"));
$difference = strtotime($shifted)-strtotime($dateTimeIn);
return $shifted . " <br> " . floor($difference/86400) . " days or " . floor($difference/3600) . " hours";
}

echo dateTimeShift($dateTimeNow, "1", "day");
?>

The current result is..

2023-01-04 09:37:51 > 19361 days or 464673 hours

I expected it to be like this

2023-01-04 09:37:51 > 1 day or 24 hours

Answer 1

The problem is that you are using the date() function without parameters, try using this:

$dateTimeNow = date("Y-m-d H:i:s");

function dateTimeShift($dateTimeIn, $lengthNum, $lengthWord) {
    $shifted = date("Y-m-d H:i:s", strtotime($dateTimeIn." + $lengthNum $lengthWord"));
    $difference = strtotime($shifted)-strtotime($dateTimeIn);
    return $shifted . " <br> " . floor($difference/86400) . " days or " . floor($difference/3600) . " hours";
}

echo dateTimeShift($dateTimeNow, "1", "day");

Output:

2023-01-04 09:57:31 <br> 1 days or 24 hours