The value of the global app economy will reach $6.3 trillion ($4.9 trillion) in 2021, up from $1.3 trillion last year.

Thats according to an App Annie report, which predicts growth in both users – up from 3.4bn in 2016, to 6.3bn in 2012 – and time spent in-app – from 1.6 trillion hours annually to 3.5 trillion.

The most eyebrow-raising figure, though, is the forecast growth in annual spend in apps per user. This is predicted to rise to $1,008 in 2021, up from $379. That might sound unlikely in a landscape dominated by in-app purchases, but the figures includes purchases made in mCommerce apps.

By 2021, China is expected to solidify its position as the biggest market for apps, growing from $790bn to to $2.6bn. In a distant second is the US, expected to hit $800bn.

However, according to the report, the most valuable users in the world come from Japan, spending an average $18.42 per hour in-app in 2021, compared to a global average of $1.81. The UK will retain its position as the third biggest spender, at a forecast $4.33 per hour, though China is closing in, at $4.29.