Generating timestamp of GMT date & time by using gmmktime function in PHP

Create a UTC timestamp with gmmktime()

Use gmmktime() when the supplied date and time components represent UTC. For new object-oriented date calculations, DateTimeImmutable with an explicit UTC timezone is usually easier to read.

$timestamp = gmmktime(12, 30, 0, 9, 14, 2026);
echo gmdate('Y-m-d H:i:s', $timestamp) . ' UTC';

This current example appears first; the detailed examples below are retained and modernized for comparison and additional use cases.

We can generate number of seconds measured since the Unix Epoch (January 1 1970 00:00:00 GMT) for any given Greenwich Mean Time GMT date and time by using gmmktime function of PHP. Here is the general syntax of mktime() function of PHP.

gmmktime (hour, minute, second, month, day, year)

Output is timestamp
This function is same as mktime() except the passed parameters represents a GMT date.

Difference in output of mktime() and gmmktime()

$d1=mktime(23,36,55,12,19,2016);
$d2=gmmktime(23,36,55,12,19,2016);
$d3=$d2-$d1;
echo " mktime(): $d1 <br> gmmktime() : $d2 <br> Difference : $d3";

Output is here

mktime(): 1482170815 
gmmktime() : 1482190615 
Difference : 19800

Other ways to get Unix Timestamp

Function	Description
strtotime()	Text string of data to timestamp
gettimestamp()	Getting Timestamp from date object

Example: Generating UTC Timestamp

$utc_time = gmmktime(12, 30, 0, 7, 10, 2023);
echo date("Y-m-d H:i:s", $utc_time);  // Output: UTC date and time

Example: Comparing gmmktime() and mktime()

$local_time = mktime(12, 30, 0, 7, 10, 2023);
$utc_time = gmmktime(12, 30, 0, 7, 10, 2023);
echo date("Y-m-d H:i:s", $local_time);  // Local time
echo '
';
echo date("Y-m-d H:i:s", $utc_time);    // UTC time

Output

2023-07-10 12:30:00
2023-07-10 14:30:00

PHP Date Functions GMT/UTC date/time Date formats for Date()

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gmmktime(): timestamp of GMT date and time