Add Estimated reading time to your WordPress blog posts

wordpress_estimated_reading_time_to_posts.php

<?php 

// functions.php


function get_reading_time($content, $words_per_minute = 300): int {
    $striped = strip_tags($content);
    $words = explode(' ', $striped);

    return round(sizeof($words) / $words_per_minute);
}

add_filter('the_content', function($content){

    if(!is_single()) {
        return $content;
    }

    $reading_time = get_reading_time($content);

    $reading_time_string = sprintf('~%d minute%s read', $reading_time, $reading_time !== 1 ? 's' : '' );

    return "<div style='margin-bottom: 2rem;'>{$reading_time_string}</div>{$content}";
}, 100, 1);