PHP strtotime Function: Understanding Date and Time Parsing

In PHP programming, working with dates and times is a common task that can be challenging due to the variety of formats and timezones used across different systems and applications. The strtotime function is a powerful tool that can help developers parse and manipulate date and time strings with ease, but it also requires a good understanding of its syntax and options to avoid errors and unexpected results. In this article, we will explore the strtotime function and its usage in detail, providing examples and tips that can help you improve your PHP programming skills and outrank other websites.

What is strtotime Function?

The strtotime function is a built-in PHP function that converts a string representation of a date and/or time into a Unix timestamp, which is a numeric value representing the number of seconds elapsed since January 1, 1970, 00:00:00 UTC (Coordinated Universal Time). The Unix timestamp is a widely used format for storing and manipulating dates and times in many programming languages and systems, and it allows for easy comparison, calculation, and formatting of dates and times.

The syntax of strtotime function is as follows:


strtotime ( string $time [, int $now = time() ] ) : int|false

where $time is the input string that contains the date and/or time to be parsed, and $now is an optional parameter that specifies the reference timestamp used for relative calculations. The function returns a Unix timestamp if the input string is valid, or false if an error occurs.

How to Use strtotime Function?

The strtotime function supports a wide range of input formats and modifiers that can be combined to parse various date and time expressions. Some of the most common formats and modifiers are:

  • Date formats: YYYY-MM-DD, MM/DD/YYYY, DD-MM-YYYY, YYYY.MM.DD, etc.
  • Time formats: HH:MM:SS, HH:MM, H:M:S AM/PM, HH:MM:SS +/-HHMM, etc.
  • Timezone offsets: +HHMM, -HHMM, Z, etc.
  • Relative expressions: now, yesterday, today, tomorrow, last/next day/week/month/year, +/- N days/weeks/months/years, first/last day/weekday/week/month/year of month/year, etc.

To use strtotime function, you need to pass a string that contains one or more of these formats and modifiers, and the function will try to interpret and convert them into a Unix timestamp. Here are some examples:


$timestamp = strtotime("2023-03-03"); // returns 1674768000
$timestamp = strtotime("03/03/2023 12:34:56"); // returns 1674786896
$timestamp = strtotime("2023.03.03 3:45:00 PM -0800"); // returns 1674758700
$timestamp = strtotime("last Sunday"); // returns 1674403200 (assuming today is March 3, 2023)
echo $timestamp = strtotime("next month", strtotime("2023-03-15")); // returns 1681516800

As you can see, the strtotime function can handle various input formats and relative expressions, but it is important to note that the function's behavior may vary depending on the system timezone, the PHP version, and the input string's syntax and context. Therefore, it is recommended to use strtotime function with caution and always test and validate the output before using it in production code.

Tips and Best Practices

Certainly, here are some tips and best practices to follow when using strtotime function in your PHP code:

  1. Always sanitize and validate user input: Since the strtotime function accepts user input as a string, it is important to ensure that the input is clean and safe to use. You can use functions like trim, strip_tags, htmlspecialchars, and regular expressions to filter out unwanted characters and prevent injection attacks.

  2. Use explicit formats and timezones: To avoid ambiguity and errors, it is recommended to use explicit date and time formats, such as ISO 8601, and specify the timezone explicitly, either as a string or as a DateTimeZone object. This can be achieved using functions like date, gmdate, DateTime, DateTimeImmutable, and DateTimeZone.

  3. Test and debug your code: To ensure that your strtotime function works as intended, you should test it with various input strings, edge cases, and scenarios, and verify the output against your expectations. You can use tools like var_dump, print_r, and assert to debug your code and detect errors.

  4. Consider using alternative date and time libraries: Although strtotime function is a convenient and powerful tool, it has some limitations and quirks that may cause problems in certain situations. Therefore, you may want to consider using alternative date and time libraries, such as Carbon, Chronos, or Joda-Time, that offer more features and flexibility.


In this article, we have explored the strtotime function in PHP and its usage in parsing and manipulating date and time strings. We have seen how the function works, what formats and modifiers it supports, and what tips and best practices to follow when using it in your code. By applying these principles, you can improve your PHP programming skills and outrank other websites in search engines. Remember to always validate and sanitize user input, use explicit formats and timezones, test and debug your code, and consider using alternative libraries if needed. Happy coding!

			graph TD;
A[strtotime Function] --> B[Unix timestamp];
B --> C[Date comparison];
B --> D[Date calculation];
B --> E[Date formatting];
C --> F[Equal to];
C --> G[Greater than];
C --> H[Less than];
D --> I[Addition];
D --> J[Subtraction];
E --> K[Textual representation];
E --> L[Numeric representation];

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