Year one, it’s a novelty. Year two—OK, it’s happening again. Year three, it’s a thing, and Amazon.com Inc. has already said there will be a Prime Day next year.

Amazon hasn’t released details and a date for the summer sales event—expect mid-July with spring ramp-ups for merchants that want to participate in the deals—but this year and the two years prior reveal Prime Day sets records for Amazon, drives a double-digit surge in sales and, most importantly, pushes more consumers to sign up for Prime memberships.

And it’s working. Consumers are increasingly signing up for Amazon’s loyalty program that costs $99 a year or $10.99 a month, with reduced rates for students and consumers receiving federal assistance. Prime includes free two-day shipping and offers customers free e-books, video streaming, photo storage and other perks. Estimates from Consumer Intelligence Research Partners as of the end of June peg Prime membership at …

To get immediate access to the rest of this article and thousands more, sign up for a free Strategy Membership using the Join for Free button below. If you’re already a member, please sign in.