From next month, Amazon’s Kindle Unlimited and Kindle Owners’ Lending Library will pay out royalties “based on the number of pages read”.

So if your book is opened on someone’s Kindle and they leave page 1 on there long enough that they could’ve read it, you get cash. It’s not entirely 1 page equals 1 payment: instead, the money comes from a pot that is shared amongst all authors whose work gets included and then gets read. Says Amazon:

Here are some examples of how it would work if the fund was $10M and 100,000,000 total pages were read in the month:
The author of a 100 page book that was borrowed and read completely 100 times would earn $1,000 ($10 million multiplied by 10,000 pages for this author divided by 100,000,000 total pages).

The author of a 200 page book that was borrowed and read completely 100 times would earn $2,000 ($10 million multiplied by 20,000 pages for this author divided by 100,000,000 total pages).

The author of a 200 page book that was borrowed 100 times but only read halfway through on average would earn $1,000 ($10 million multiplied by 10,000 pages for this author divided by 100,000,000 total pages).

Kindle Unlimited Pages Read – Amazon

It’s that bit about a page not actually being read, there’s no way to know that, but it needs to be open on the Kindle for long enough that it could have been. There’s got to be a way to game that.

Read the full Amazon detail, though be warned it’s (possibly deliberately) the most boring thing you’ll see today.