Freemium apps, free apps that let users purchase additional content, are on the rise in both iOS and Google Play stores, according to a new report from App Annie, a data and analytics company dedicated to measuring app consumption.

Here is more from App Annie’s blog: “Over the last 24 months, worldwide revenues for freemium apps on iOS have more than quadrupled. In 2012, worldwide freemium revenues on Google Play have grown 3.5X. Premium revenues for both app stores remained relatively flat in these time periods.”

In the U.S. freemium apps are rising at a steady pace. The rate of growth is huge in China and Japan. In Japan, Google Play freemium revenues have risen 24x in the last year and a half. In China, iOS freemium revenues have grown almost 25X in the past year and a half.