Why don't my skills stay golden?

How does Duolingo's algorithm work? How does it know when I have to strengthen my skills? Is it based on any science? Is it personalized? How smart is Duolingo?

We are indeed science-based and use machine learning to calculate when you should be exposed to certain new skills and when it is time to look over old ones again so that words stay fresh and golden in your brain, —and so your language skills stay polished in order for you to advance with confidence.

If you are interested in learning about the science behind strength meters, forgetting curves, half-life regression, and so on, there is a more scientific explanation in our blog Making Duolingo that will be right up your alley!