Through tonight only, buy a Kindle eBook today, earn 40% credit back towards your next book, up to a maximum of $20. Offer valid only once per customer. Credit must be redeemed by July 25, 2017. Credit can be redeemed on Print books sold by Amazon.com and Kindle eBooks. Within 24 hours of your purchase, you will receive an email that indicates the promotional credit has been added to your account. Terms and conditions below.