onlineth

A pluginized version of ReadRemaining.js
Tell your readers how long they’ll need to get through all of your gibberish, with this clever jQuery plugin. With WP ReadRemaining TL;DR is a thing of the past.
Personalized – The time is estimated based on the user scrolling speed Non-Annoying – It is set to appear only when the user is actually reading. 
Fully customizable – Bold Comic Sans? No problem, just set the css. But… why? 
Flexible layout – Takes into account text, images or even videos.

WP ReadRemaining

This WordPress plugin allows you to show the user how long it will take to read the article considering the speed in which the user is scrolling.

brianmcculloh

A very unobtrusive and light-weight reading progress bar indicator showing the user how far scrolled through the current post or page they are. You can control placement and color of the progress bar, and you can choose whether it includes just the main content or also the comments.
The progress bar only displays once the user begins scrolling the page so it is as unobtrusive as possible. Once the user stops scrolling or scrolls down past the content the progress bar subtly mutes until it is needed again.
There is also a reading time commitment feature that you can separately enable. Control the placement (above or below title, or above content), style, and whether it displays on posts and/or pages. Uses 200wpm as the metric for average reading time.
You can also place the time commitment label anywhere you want via the [wtr-time] shortcode.

Worth The Read

Looks very promising, but on my site, nothing was added.

Absolutely does not anything :(

An adjustable progress meter showing how much of the post/page the user has scrolled through, and a read time commitment label near the post titles.

WP ReadRemaining vs Worth The Read