Two teenagers have made an app that tells you how many calories you have on your plate and made €2 million in one month alone.

Cal AI, the app created by Zach Yadegari and his co-founder Henry Langmack, both just 18 years old, has quickly become popular, with more than 5 million downloads in just eight months since its launch.

Cal AI works on a very simple principle: you take a photo of the food on your plate, and the app estimates your calories and macronutrients.