What is it?
PHP's date and time functions let you format timestamps for display, calculate differences between dates, convert natural language to timestamps, and handle timezones.
Why does it matter?
Almost every application involves dates — order timestamps, subscription expiry, user birthdays, event schedules. Getting dates wrong causes billing errors, expired coupons that still work, and appointment clashes.
Learn PHP date(), strtotime(), and DateTime class for formatting, comparing, and calculating dates.
Real-World Use Cases
- 📅 Subscription expiry - Calculate if a subscription has expired by comparing the stored end_date with today using DateTime::diff().
- 🎂 Birthday reminders - Find users whose birthday is today using CURDATE() in SQL, then send them a greeting from PHP.
- 📊 Monthly reports - Use strtotime('-1 month') to get the start and end of last month for date-range report queries.
- ⏰ Scheduled emails - Store scheduled_at as DATETIME in the database, then use PHP's date comparison to find emails due to be sent.
date() Function — Format Timestamps
echo date("Y-m-d");
// 2026-05-25
//with time
echo date("d-m-Y", time());Common formats:
Y→ 4-digit yearm→ monthd→ dayH→ houri→ minutess→ seconds
strtotime — Natural Language to Timestamp
echo strtotime("tomorrow");
echo date("Y-m-d", strtotime("+7 days"));
echo date("Y-m-d", strtotime("next Monday"));DateTime Class — Object-Oriented Approach
$date = new DateTime();
echo $date->format("Y-m-d");Q: What format should I use to store dates in MySQL?
Always use DATETIME or DATE column types, never strings. Use date('Y-m-d H:i:s') when inserting from PHP. Never store as d/m/Y strings — you cannot sort or compare them correctly.
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