Every Kindle owner needs to know about this free Prime Day upgrade – but you must act fast, it runs out today!

I've now spent hours scouring Amazon Prime Day sales, and I've just come across an offer that's really a must-buy for owners of the best Kindles – and one that I think I'm going to take up myself.

It's three months free of Amazon Kindle Unlimited, which would usually set you back £9.49 per month. That means you're making a saving of £28.47, but you need to act really fast, because the offer is only valid until midnight tonight, Friday 11 July (and it's only for Prime Subscribers, of course).

Kindle Unlimited for three months: was £28.47 at Amazon

Kindle Unlimited is now free for three months, so you can see for yourself whether it's something that's going to suit you. You can access all of this content across any Kindle device or though any Kindle app.

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If you're new to Kindle Unlimited, it's more or less what it sounds like: as many ebooks and audiobooks as you like, all for one flat monthly fee (or for no fee at all, in this case). You'll never be stuck for something to read or listen to again.

Whenever I finish an ebook on my own Amazon Kindle Paperwhite, I can spend many minutes browsing through the Amazon store looking for something else to read – and checking whether the price of the title fits within my budget.

With this special offer, you can essentially read as much as you want over the course of three months, without paying anything. There are millions of ebooks and thousands of audiobooks to choose from in the Unlimited library.

Note that you will be automatically subscribed to Kindle Unlimited at £9.49 for the fourth month and onwards, though you can cancel before then.