Apple customers have downloaded more than 40 billion apps, with two billion-plus just in December.
And half of the total – 20 billion – were downloaded in 2012 on iPhones, iPods or iPod Touch.
The 10 billion milestone came in early 2011 and the 25 billion mark in March last year.
Updates or re-downloads are not included.
Apple's app store, which opened in 2008, has more than 500 million active accounts and 775,000 individual apps are available.
The company says it has so far paid more than $US7 billion to app developers.
By the end of 2012, 25 billlion Google Android apps had been downloaded - 15 billion of them over the past 12 months.