Date & Time Functions

PHP provides powerful tools for working with dates and times, from simple procedural functions to the robust DateTime class. This guide covers both approaches.

PHP Date/Time Functions - Full Documentation ↗

Getting Current Date & Time

time() - Get Unix Timestamp

Returns the current Unix timestamp (seconds since January 1, 1970).

$timestamp = time();
echo $timestamp;  // e.g., 1703001600

// Useful for comparisons and calculations
$futureTime = time() + 3600;  // 1 hour from now
$pastTime = time() - 86400;   // 24 hours ago

date() - Format Current Date/Time

Formats a timestamp (or current time) into a readable string.

// Current date and time
echo date('Y-m-d');        // 2024-12-19
echo date('H:i:s');        // 14:30:45
echo date('Y-m-d H:i:s');  // 2024-12-19 14:30:45

// Format a specific timestamp
$timestamp = 1703001600;
echo date('Y-m-d', $timestamp);  // 2023-12-19

DateTime Class - Object-Oriented Approach

// Current date and time
$now = new DateTime();
echo $now->format('Y-m-d H:i:s');  // 2024-12-19 14:30:45

// Specific date
$date = new DateTime('2024-12-25');
echo $date->format('l, F j, Y');   // Wednesday, December 25, 2024

---

Date Format Characters

Common Format Characters

Character	Description	Example
Year
Y	4-digit year	2024
y	2-digit year	24
Month
m	Month (01-12)	01, 12
n	Month (1-12)	1, 12
F	Full month name	January
M	Short month name	Jan
Day
d	Day (01-31)	01, 31
j	Day (1-31)	1, 31
l	Full day name	Monday
D	Short day name	Mon
Time
H	Hour 24-format (00-23)	00, 23
h	Hour 12-format (01-12)	01, 12
i	Minutes (00-59)	00, 59
s	Seconds (00-59)	00, 59
A	AM/PM	AM, PM
a	am/pm	am, pm
Other
U	Unix timestamp	1703001600
N	Day of week (1-7)	1 (Monday)
w	Day of week (0-6)	0 (Sunday)
W	Week number	51
t	Days in month	28, 31

Common Format Patterns

$date = new DateTime('2024-12-19 14:30:45');

// Database format
echo $date->format('Y-m-d H:i:s');     // 2024-12-19 14:30:45

// Human-readable formats
echo $date->format('F j, Y');          // December 19, 2024
echo $date->format('l, F j, Y');       // Thursday, December 19, 2024
echo $date->format('M j, Y g:i A');    // Dec 19, 2024 2:30 PM

// ISO 8601 format
echo $date->format('c');               // 2024-12-19T14:30:45+00:00

// RFC 2822 (email dates)
echo $date->format('r');               // Thu, 19 Dec 2024 14:30:45 +0000

// Custom formats
echo $date->format('d/m/Y');           // 19/12/2024
echo $date->format('m-d-Y');           // 12-19-2024

---

Parsing Dates

strtotime() - Parse English Text to Timestamp

Converts date/time strings into Unix timestamps.

// Absolute dates
echo strtotime('2024-12-25');              // Unix timestamp
echo strtotime('December 25, 2024');       // Same result
echo strtotime('25 December 2024');        // Same result

// Relative dates (from current time)
echo strtotime('now');                     // Current timestamp
echo strtotime('today');                   // Today at midnight
echo strtotime('tomorrow');                // Tomorrow at midnight
echo strtotime('yesterday');               // Yesterday at midnight

// Relative adjustments
echo strtotime('+1 day');                  // Tomorrow
echo strtotime('+1 week');                 // 7 days from now
echo strtotime('+2 weeks 3 days');         // 17 days from now
echo strtotime('-1 month');                // 1 month ago
echo strtotime('+1 year');                 // 1 year from now

// Time adjustments
echo strtotime('+3 hours');                // 3 hours from now
echo strtotime('-30 minutes');             // 30 minutes ago

// Specific day references
echo strtotime('next Monday');             // Next Monday
echo strtotime('last Friday');             // Last Friday
echo strtotime('first day of next month'); // First of next month
echo strtotime('last day of this month');  // Last day of current month

// Combining with date()
echo date('Y-m-d', strtotime('+1 week'));  // 2024-12-26
echo date('Y-m-d', strtotime('next Monday')); // Next Monday's date

DateTime::createFromFormat() - Parse with Specific Format

Parse dates with a known format (more reliable than strtotime()).

// Parse various formats
$date1 = DateTime::createFromFormat('Y-m-d', '2024-12-19');
$date2 = DateTime::createFromFormat('d/m/Y', '19/12/2024');
$date3 = DateTime::createFromFormat('m-d-Y H:i', '12-19-2024 14:30');

echo $date1->format('F j, Y');  // December 19, 2024
echo $date2->format('F j, Y');  // December 19, 2024
echo $date3->format('F j, Y g:i A');  // December 19, 2024 2:30 PM

// Handle parsing errors
$date = DateTime::createFromFormat('Y-m-d', 'invalid-date');
if ($date === false) {
    $errors = DateTime::getLastErrors();
    print_r($errors);  // Shows parsing errors
}

// Parse with timezone
$date = DateTime::createFromFormat(
    'Y-m-d H:i:s',
    '2024-12-19 14:30:00',
    new DateTimeZone('America/New_York')
);

---

DateTime Class (Modern Approach)

Creating DateTime Objects

// Current date/time
$now = new DateTime();

// From string
$date1 = new DateTime('2024-12-25');
$date2 = new DateTime('2024-12-25 14:30:00');
$date3 = new DateTime('next Monday');
$date4 = new DateTime('+1 week');

// From timestamp
$date = new DateTime();
$date->setTimestamp(1703001600);

// With timezone
$date = new DateTime('now', new DateTimeZone('Europe/London'));

DateTime vs DateTimeImmutable

DateTime modifies the object in place, while DateTimeImmutable returns a new object.

// DateTime - modifies original
$date = new DateTime('2024-12-19');
$date->modify('+1 day');
echo $date->format('Y-m-d');  // 2024-12-20 (original changed)

// DateTimeImmutable - returns new object
$date = new DateTimeImmutable('2024-12-19');
$newDate = $date->modify('+1 day');
echo $date->format('Y-m-d');     // 2024-12-19 (unchanged)
echo $newDate->format('Y-m-d');  // 2024-12-20 (new object)

Best Practice

Use DateTimeImmutable when you want to prevent accidental modifications, especially when passing dates to functions.

Modifying Dates

$date = new DateTime('2024-12-19');

// Using modify() - accepts strtotime() strings
$date->modify('+1 day');
$date->modify('+2 weeks');
$date->modify('next Monday');

// Using setDate(), setTime()
$date->setDate(2024, 12, 25);       // Set to Dec 25, 2024
$date->setTime(14, 30, 0);          // Set to 2:30 PM

// Get individual components
echo $date->format('Y');  // Year
echo $date->format('m');  // Month
echo $date->format('d');  // Day

Comparing Dates

$date1 = new DateTime('2024-12-19');
$date2 = new DateTime('2024-12-25');

// Direct comparison
if ($date1 < $date2) {
    echo "Date1 is earlier";
}

if ($date1 == $date2) {
    echo "Dates are equal";
}

if ($date1 > $date2) {
    echo "Date1 is later";
}

// Compare timestamps
if ($date1->getTimestamp() < $date2->getTimestamp()) {
    echo "Date1 is earlier";
}

---

Date Arithmetic

Using strtotime() for Simple Calculations

// Add/subtract time
$nextWeek = date('Y-m-d', strtotime('+1 week'));
$lastMonth = date('Y-m-d', strtotime('-1 month'));

// From a specific date
$baseDate = '2024-12-19';
$future = date('Y-m-d', strtotime($baseDate . ' +10 days'));
echo $future;  // 2024-12-29

DateInterval Class

Represents a duration of time.

// Create intervals
$interval1 = new DateInterval('P1D');      // 1 day
$interval2 = new DateInterval('P2W');      // 2 weeks
$interval3 = new DateInterval('P1M');      // 1 month
$interval4 = new DateInterval('P1Y');      // 1 year
$interval5 = new DateInterval('PT1H');     // 1 hour
$interval6 = new DateInterval('PT30M');    // 30 minutes
$interval7 = new DateInterval('P1Y2M3D');  // 1 year, 2 months, 3 days
$interval8 = new DateInterval('P1DT12H');  // 1 day, 12 hours

// Interval format: P[years]Y[months]M[days]DT[hours]H[minutes]M[seconds]S

DateTime::add() and DateTime::sub()

$date = new DateTime('2024-12-19');

// Add time
$date->add(new DateInterval('P10D'));  // Add 10 days
echo $date->format('Y-m-d');  // 2024-12-29

// Subtract time
$date->sub(new DateInterval('P1M'));   // Subtract 1 month
echo $date->format('Y-m-d');  // 2024-11-29

// Chain operations (with DateTimeImmutable)
$date = new DateTimeImmutable('2024-12-19');
$result = $date
    ->add(new DateInterval('P1M'))
    ->add(new DateInterval('P5D'));
echo $result->format('Y-m-d');  // 2025-01-24

DateTime::diff() - Calculate Differences

$date1 = new DateTime('2024-01-01');
$date2 = new DateTime('2024-12-25');

$diff = $date1->diff($date2);

echo $diff->days;    // Total days: 359
echo $diff->y;       // Years: 0
echo $diff->m;       // Months: 11
echo $diff->d;       // Days: 24

// Format the difference
echo $diff->format('%y years, %m months, %d days');
// Output: 0 years, 11 months, 24 days

echo $diff->format('%a total days');
// Output: 359 total days

// Check if date is in past or future
if ($diff->invert === 1) {
    echo "Date1 is after Date2";
} else {
    echo "Date1 is before Date2";
}

---

Timezone Handling

Setting Default Timezone

// Set default timezone for all date functions
date_default_timezone_set('America/New_York');

// Get current timezone
echo date_default_timezone_get();  // America/New_York

DateTimeZone Class

// Create timezone objects
$nyTz = new DateTimeZone('America/New_York');
$londonTz = new DateTimeZone('Europe/London');
$tokyoTz = new DateTimeZone('Asia/Tokyo');

// Create date with specific timezone
$date = new DateTime('now', $nyTz);
echo $date->format('Y-m-d H:i:s T');  // 2024-12-19 09:30:00 EST

// Get timezone offset
echo $nyTz->getOffset($date) / 3600;  // -5 (hours from UTC)

Converting Between Timezones

// Create a date in New York timezone
$nyDate = new DateTime('2024-12-19 14:00:00', new DateTimeZone('America/New_York'));
echo $nyDate->format('Y-m-d H:i:s T');  // 2024-12-19 14:00:00 EST

// Convert to London timezone
$nyDate->setTimezone(new DateTimeZone('Europe/London'));
echo $nyDate->format('Y-m-d H:i:s T');  // 2024-12-19 19:00:00 GMT

// Convert to Tokyo timezone
$nyDate->setTimezone(new DateTimeZone('Asia/Tokyo'));
echo $nyDate->format('Y-m-d H:i:s T');  // 2024-12-20 04:00:00 JST

List Available Timezones

// Get all timezone identifiers
$timezones = DateTimeZone::listIdentifiers();

// Get timezones by region
$usTimezones = DateTimeZone::listIdentifiers(DateTimeZone::AMERICA);
$euroTimezones = DateTimeZone::listIdentifiers(DateTimeZone::EUROPE);

---

Practical Examples

Age Calculation

function calculateAge(string $birthdate): int {
    $birth = new DateTime($birthdate);
    $today = new DateTime('today');
    $age = $birth->diff($today);
    return $age->y;
}

echo calculateAge('1990-05-15');  // e.g., 34

// More detailed version
function getAgeDetails(string $birthdate): array {
    $birth = new DateTime($birthdate);
    $today = new DateTime('today');
    $diff = $birth->diff($today);

    return [
        'years' => $diff->y,
        'months' => $diff->m,
        'days' => $diff->d,
        'total_days' => $diff->days
    ];
}

Date Validation

function isValidDate(string $date, string $format = 'Y-m-d'): bool {
    $d = DateTime::createFromFormat($format, $date);
    return $d && $d->format($format) === $date;
}

var_dump(isValidDate('2024-12-19'));    // true
var_dump(isValidDate('2024-13-19'));    // false (invalid month)
var_dump(isValidDate('2024-02-30'));    // false (invalid day)
var_dump(isValidDate('19/12/2024', 'd/m/Y'));  // true

Working with Database Dates

// Storing to database (MySQL DATETIME format)
$date = new DateTime();
$dbFormat = $date->format('Y-m-d H:i:s');
// Use in INSERT: ... VALUES ('$dbFormat')

// Reading from database
$dbDate = '2024-12-19 14:30:00';
$date = new DateTime($dbDate);
echo $date->format('F j, Y g:i A');  // December 19, 2024 2:30 PM

// Handle NULL dates
function formatDbDate(?string $dbDate, string $format = 'M j, Y'): string {
    if ($dbDate === null || $dbDate === '0000-00-00') {
        return 'N/A';
    }
    return (new DateTime($dbDate))->format($format);
}

Formatting for Display

function formatDateForDisplay(string $date, string $style = 'medium'): string {
    $dt = new DateTime($date);

    return match($style) {
        'short' => $dt->format('m/d/Y'),           // 12/19/2024
        'medium' => $dt->format('M j, Y'),         // Dec 19, 2024
        'long' => $dt->format('F j, Y'),           // December 19, 2024
        'full' => $dt->format('l, F j, Y'),        // Thursday, December 19, 2024
        'datetime' => $dt->format('M j, Y g:i A'), // Dec 19, 2024 2:30 PM
        'relative' => getRelativeTime($dt),
        default => $dt->format('Y-m-d')
    };
}

function getRelativeTime(DateTime $date): string {
    $now = new DateTime();
    $diff = $now->diff($date);

    if ($diff->days === 0) {
        return 'Today';
    } elseif ($diff->days === 1 && $diff->invert === 1) {
        return 'Yesterday';
    } elseif ($diff->days === 1 && $diff->invert === 0) {
        return 'Tomorrow';
    } elseif ($diff->days < 7) {
        return $diff->invert ? "{$diff->days} days ago" : "In {$diff->days} days";
    } else {
        return $date->format('M j, Y');
    }
}

Date Range Iteration

// Iterate through a date range
$start = new DateTime('2024-12-01');
$end = new DateTime('2024-12-07');
$interval = new DateInterval('P1D');

$period = new DatePeriod($start, $interval, $end);

foreach ($period as $date) {
    echo $date->format('Y-m-d') . "\n";
}
// Output: 2024-12-01 through 2024-12-06

// Include end date
$period = new DatePeriod($start, $interval, $end->modify('+1 day'));

---

Quick Reference

Common Functions

Function	Purpose	Example
time()	Current timestamp	time()
date($format, $ts)	Format timestamp	date('Y-m-d')
strtotime($str)	Parse to timestamp	strtotime('+1 week')
mktime(...)	Create timestamp	mktime(12, 0, 0, 12, 25, 2024)
checkdate($m, $d, $y)	Validate date	checkdate(12, 25, 2024)

DateTime Methods

Method	Purpose
format($format)	Format as string
modify($str)	Modify date
add($interval)	Add interval
sub($interval)	Subtract interval
diff($date)	Calculate difference
setTimezone($tz)	Change timezone
getTimestamp()	Get Unix timestamp
setTimestamp($ts)	Set from timestamp

DateInterval Format

P[n]Y[n]M[n]DT[n]H[n]M[n]S

P = Period (required)
nY = Years
nM = Months
nD = Days
T = Time separator (required before time components)
nH = Hours
nM = Minutes
nS = Seconds

Examples:
P1D = 1 day
P2W = 2 weeks
P1M = 1 month
PT1H = 1 hour
P1Y2M3DT4H5M6S = 1 year, 2 months, 3 days, 4 hours, 5 minutes, 6 seconds