Android may have Apple beat when it comes to total market share and number of app downloads, but Cupertino is still ahead of Google in terms of revenue generated from app sales. According to a report from App Annie, however, Android app revenue will surpass that of iOS for the first time by the end of this year – if third-party stores, not just Google Play, are taken into account.

Apple made $34 billion on 29 billion app downloads in 2016, whereas Google made $17 billion on 63 billion downloads during the same period. This year, iOS app sales are predicted to generate $40 billion, and Google Play downloads are expected to bring in $21 billion.

Third-party Android stores, such as those from Amazon, Samsung, Tencent, Baidu, and Xiaomi continue to grow. After making $10 billion last year, these marketplaces are predicted to generate $20 billion in 2017. Add that figure to Google Play’s predicted 2017 earnings, and it comes to $41 billion for all Android downloads, more than Apple’s revenue for this year.

App Annie estimates that there will be a total of 197 billion apps downloaded across all platforms this year, while total revenue will reach $82.2 billion. By 2021, it’s predicted to reach 352.9 billion downloads and generate $139.1 billion.

What’s interesting about the figures is the way Apple continues to make more money from its store than Google Play despite recording fewer downloads. If App Annie is correct, Apple will generate almost double the revenue of Google Play this year, despite having only a fraction of the downloads – it seems iOS users are more willing, and more able, to spend cash on apps. But the Android App market is growing at a rapid pace, especially in China and emerging markets such as India, Mexico, Brazil, and Indonesia.