# How to Get the Date/Time Difference in Seconds Between Two DateTime Objects in PHP?

By default there's no method available on the `DateTime` or `DateInterval` class to get the difference between two `DateTime` objects in seconds. Therefore, you can either get the difference of the timestamps of the two dates or calculate the number of seconds yourself:

## Comparing Timestamps to Get Number of Seconds Between Two Dates

We can simply compare timestamps of two dates to get the difference in seconds. For example:

```\$start = new DateTime('2011-12-31 00:00:00');
\$end = new DateTime('2021-01-01 00:00:00');

echo \$end->getTimestamp() - \$start->getTimestamp(); // output: 284169600
```

Please note that comparing timestamps could lead to problems with dates before 1970 and after 2038.

## Calculating Number of Seconds Between Two Dates

You can calculate the number of seconds between the two dates in the following way:

```\$start = new DateTime('2011-12-31 00:00:00');
\$end = new DateTime('2021-01-01 00:00:00');
\$diff = \$start->diff(\$end);

\$daysInSecs = \$diff->format('%r%a') * 24 * 60 * 60;
\$hoursInSecs = \$diff->h * 60 * 60;
\$minsInSecs = \$diff->i * 60;

\$seconds = \$daysInSecs + \$hoursInSecs + \$minsInSecs + \$diff->s;

echo \$seconds; // output: 284169600
```

The calculation works in the following way:

• Using the `%r` formatting character, adds the minus sign when the result is negative;
• Using the `%a` formatting character gives us the total number of days between two dates;
• Using the `%r%a` format together, we can get the negative/positive number of days. Using that, we can convert the number of days into seconds by multiplying it with hours in a day, minutes in an hour, and seconds in a minute (i.e. `days * 24 * 60 * 60`);
• The calculation in the last step does not take into account the hours, minutes and seconds in the date difference (as they're not included in the `%a` format). To include those, we simply use the hour, minute and second properties available on the `DateInterval` object and convert them into seconds as shown in the example above.

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