| raw | raw/how-i-built-it-400k-month-mobile-app.md |
|---|---|
| url |
TL;DR
Julian, a software developer from Argentina based in Australia, cloned a popular fitness app’s UI/UX, built a much safer and robust workout engine, and scaled Gravel to over $440K/month in revenue and 70,000+ active subscribers using early Reddit validation and localized Meta/TikTok paid ads.
The Founder’s Story
Julian grew up in Argentina, where his father owned a fitness center, instilling in him a lifelong passion for sports and the gym. After studying software engineering, he moved to Australia, working for startups, large tech firms like Atlassian, TV channels, and an investment fund.
His entrepreneurial journey started with a failed influencer marketing startup with his best friend Matias and co-founder Aaron. Although it pivoted into a non-scalable marketing agency that they eventually abandoned, the experience taught them critical lessons about user acquisition, metrics, and the lucrative potential of mobile apps—especially fitness apps.
The Building Process
Motivated to build something scalable, Julian initially worked on a generic workout tracker similar to Heavy or Strong. Feeling it lacked unique value, his co-founder showed him Fitbod, a leading workout app. Julian realized Fitbod’s workouts were often poorly structured and even dangerous.
This became the catalyst: they decided to rebuild the Fitbod UI/UX concept backed by a proper, safe workout engine.
- MVP Timeline: It took 2 to 3 months to build the initial MVP.
- Complexity: The main challenge was the complex business logic of the workout engine—taking into account user equipment, weekly goals, consistency, gender, weight, age, and gym configurations.
Launch & Marketing Strategy
Gravel’s growth can be split into two primary phases: validation/early traction and paid scaling.
- Reddit Validation: Julian posted about the app (originally named Games AI or Gyms AI) on Reddit, sharing its technical specifications. The thread gained 300,000+ impressions and a couple of hundred upvotes in the first few hours. This brought in their first few thousand users—mostly tech-minded developers who loved the gym but felt intimidated by it. This early community provided crucial bug reports and validated their product-market fit for free.
- Paid Ads & Geo-Arbitrage: Once a subscription model was added, Julian turned on paid ads and secured their first paying subscriber within 10 minutes.
- Local Translation: Because the founders spoke Spanish, they translated the app and targeted South American markets. Paid ads there were incredibly cheap (spending under $50/day initially) and had far lower competition than the US market.
- UGC and AI Creatives: User-Generated Content (UGC) was their highest-converting ad format. They hired creators for as low as $50/video and leveraged AI video generators and CapCut to maintain a high volume of cheap, easily testable ad variations.
- Meta Ads Library Hack: They extensively audited their competitors’ public campaigns on the Meta Ads Library, copied their high-performing layouts and copy structures, and adapted them.
Operational & Pricing Tactics
- Hard Paywall: Gravel utilizes a hard, unskippable paywall right after the onboarding questionnaire before users can access the dashboard.
- 24/7 Human Support: The app features an in-app support chat handled by real people, not AI. This high-touch service acts as a primary retention driver.
- Onboarding Experience: Extensive personalized onboarding (asking for goals, level, one-rep max, excluded muscles) demonstrates value and builds buy-in before presenting the paywall.
Tech Stack & Tools
- Frontend: React Native & Expo
- Backend: .NET (C#) for core business and workout engine logic
- Dashboards: Next.js & React (internal admin dashboards)
- AI/Assistance: Cursor (used selectively on specific files to prevent “rogue” AI generations)
Key Stats & Metrics
- Monthly Revenue: $440,000+ (over $4.8M ARR)
- Active Subscribers: 70,000+
- MVP Build Time: 2–3 months
- Early Paid Ad Budget: <$50/day (South America)
- Ad Spend Margin: Paid ads account for approximately one-third of total revenue.
- Team Size: Expanded from 3 co-founders to 13–14 team members (including contractors/part-timers).
- Other Expenses: ~15% Apple App Store commission, 1% payment processing/other clip, $1,000/mo infrastructure & server bills, $1,000/mo MMP.
Related Frameworks & Playbooks
- reddit-marketing — Reddit organic growth and community Q&A funnels
- mobile-app-monetization — Paywall optimization, hard paywalls, and pricing metrics