The Wonder Weeks

Turning a parenting bestseller into a 5-star subscription app

A bestselling book in need of a digital equivalent

The Wonder Weeks is based on the Dutch book Oei, ik groei! by physical anthropologist Hetty van de Rijt and developmental psychologist Frans Plooij.

This book is a parenting guide that’s sold more than 2 million copies and been translated into over 20 languages since its original 1992 publication. It helps parents understand why their baby cries, mapping the predictable “leaps” behind a baby’s fussiest phases.

Apadmi’s team in the Netherlands built the earlier versions of the app, which went on to become the best-selling app in its category, rated 4.9 stars from over 109,000 reviews and available in 16 languages.

Off the back of that success, The Wonder Weeks asked Apadmi to build the next iteration: a subscription model, community integration, and cross-platform account sharing, ready for a worldwide release.

Rebuilt around research, not assumptions

The redesign started with user research and testing, not guesswork.

That research surfaced a clear need: parents wanted certainty when their own experience fell short, and connection with other, more experienced parents to fill the gap. The rebuild was shaped around answering both.

From one-off purchase to sustainable subscription

The app moved from a single-purchase model to a subscription, giving The Wonder Weeks more flexible payment options and a foundation to keep growing the business.

One account for the whole family

Cross-platform account sharing lets parents, grandparents and nannies alike contribute to the same baby diary, use the monitor features, and draw on the app’s full knowledge base together.

Onboarding tested, not guessed

A subscription model lives or dies on a frictionless first impression, so multiple onboarding journeys were tested and continue to be refined through ongoing A/B testing, with the iOS experience built in close collaboration with Apple.

From local to global

The rebuilt app launched worldwide and significantly grew revenue, as well as an increase in iOS and Android downloads.

+90%

revenue growth
+150%

increase in iOS downloads
+100%

increase in Android downloads

Impact: Satisfied customers are retained customers

With the subscription model live, the priority shifted to retention: continuing to deliver value that justifies an ongoing relationship rather than a one-off download. New features deepen interaction between users, support user-generated content, and build out richer parent profiles.

“One thing I appreciate about The Wonder Weeks app is the baby playtime prompts provided for each leap. My daughter is currently 12 weeks old, and I’ve been enjoying playing the suggested ‘games’ with her as a way to help her get the most out of each leap. It makes me feel like I’m giving her exactly what she needs regarding both entertainment and cognitive stimulation as she develops.”

– Emilee Janitz, Parent and writer for The Everymom