Stuff & Things Reading Estimate adds a small, unobtrusive “X min read” estimate to your posts so readers know what they’re getting into.
[reading_time] shortcode.%s min read, About %s minutes).That’s the whole plugin. No accounts, no upsells, no external services, nothing phoned home. The estimate is calculated on your server from the post’s word count.
Word count = the post content with HTML and shortcodes stripped, divided by your words-per-minute setting, rounded up (minimum 1 minute).