How to Customize WordPress User Registration: Adding Custom Fields and Validation

In this comprehensive tutorial, we’ll guide you through refining the user sign-up experience on your WordPress site. We’ll introduce additional form fields, including a dedicated one for phone numbers, and implement stringent validation to ensure accurate user data entry. By following these meticulously outlined steps, you’ll not only personalize the sign-up process but also enhance its security. Let’s start the journey to elevate your WordPress sign-up seamlessly and professionally.

Before proceeding with any customizations in WordPress, it’s essential to set up a child theme. A child theme acts as a safe and efficient way to make modifications without affecting the parent theme. If you haven’t set up a child theme yet, follow this tutorial on How to Create a Child Theme for Customization. It will guide you through the process and ensure that your customizations remain intact even after theme updates.

Adding Custom Fields

Open your child theme’s functions.php file and utilize the register_form hook to seamlessly inject additional fields into the registration form. Let’s consider the addition of a “Phone Number” field:

function custom_register_fields() {
		<label for="phone_number"><?php esc_html_e( 'Phone Number', 'your-text-domain' ); ?><br>
			<input type="text" name="phone_number" id="phone_number" class="input" value="<?php echo esc_attr( $_POST['phone_number'] ); ?>" size="25" />
add_action( 'register_form', 'custom_register_fields' );
Code language: PHP (php)


Here, we introduce the concept of a child theme by placing our customization in the functions.php file of the child theme. The register_form hook allows us to insert HTML directly into the user registration form. The added HTML includes a label and input field for the phone number, and the esc_attr function ensures secure handling of the input value. To make the “Phone Number” field required, add the “required” attribute to the input field.

Implement Validation for Custom Fields

To ensure the submitted data meets specific criteria, use the registration_errors hook. Below is an example validating the phone number:

function custom_enhanced_validation( $errors ) {
	if ( empty( $_POST['phone_number'] ) ) {
		$errors->add( 'phone_number_error', __( 'Phone number is required.' ) );
	} elseif ( ! preg_match( '/^\d+$/', $_POST['phone_number'] ) ) {
		$errors->add( 'phone_number_error', __( 'Invalid phone number format. It should contain only numeric characters.', 'your-text-domain' ) );
	return $errors;
add_filter( 'registration_errors', 'custom_enhanced_validation', 10, 1 );
Code language: PHP (php)


This modification includes preg_match in the basic validation, ensuring the phone number contains only numeric characters. If any non-numeric characters are found, an error is added to the registration errors.

Explanation of preg_match:

The preg_match function in PHP is a powerful tool for performing regular expression matching. In our context, /^\d+$/ is the regular expression used. Here’s what each part means:

  • ^: Asserts the start of the string.
  • \d: Matches any digit (equivalent to [0-9]).
  • +: Requires at least one or more occurrences of the preceding digit.
  • $: Asserts the end of the string.

So, preg_match('/^\d+$/', $_POST['phone_number']) checks if the provided phone number consists of at least one or more numeric digits, ensuring it contains only numbers.

Add Optional Advanced Validation

Consider adding optional advanced validation to your WordPress user registration for precision. This is especially useful for verifying the total number of digits in fields like phone numbers. Ensuring a consistent data format, such as a minimum of 10 digits, enhances accuracy, prevents errors, and provides a more reliable registration experience. Add this to your functions.php:

function custom_advanced_validation( $errors ) {
	if ( ! empty( $_POST['phone_number'] ) ) {
		if ( ! preg_match( '/^\d+$/', $_POST['phone_number'] ) ) {
			$errors->add( 'phone_number_error', __( 'Invalid phone number format. It should contain only numeric characters.', 'your-text-domain' ) );
		} else {
			$digit_count = strlen( $_POST['phone_number'] );
			if ( $digit_count < 10 ) {
				$errors->add( 'phone_number_error', __( 'Phone number should have at least 10 digits.', 'your-text-domain' ) );
	return $errors;
add_filter( 'registration_errors', 'custom_advanced_validation', 11, 1 );
Code language: PHP (php)


In this additional check, it first ensures that the phone number contains only numeric characters using preg_match. If the format is correct, it then counts the total number of digits. If the count is less than 10, an error is added to the registration errors.

Testing the Customized User Registration

Navigate to your registration page to thoroughly test the new “Phone Number” field and validation mechanisms within your child theme. Verify that your customizations work as expected.

That’s it! You’ve now implemented enhanced validation for the WordPress user registration process. The basic validation checks for numeric characters, while the advanced validation includes an extra check on the total number of digits. This ensures a more comprehensive and secure registration experience for your site’s visitors.

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