$400/Month From a Dead-Simple Fasting Calculator

A solo founder in the US built a tool that does one thing… tell you when to eat.

You enter your last meal time, pick a fasting method (16:8, OMAD, whatever), and the calculator instantly shows your fasting window and next meal time. No signup, no app to download.

Earnings via Google ads… apparently $400/month, mostly passive 🤑

Costs are basically a domain and cheap hosting, so it’s nearly all profit.

The clever part isn’t the calculator. It’s the cluster. The site has quietly stacked ~10 related tools – BMR, body fat, a fasting timer, printable templates – each catching its own slice of search traffic 👀

It’s a proven play: build one genuinely useful tool around something people Google, slap display ads on it, then add more tools off the same audience.

But now you can vibe-code something like this in a weekend. Pick any number people search for – mortgage payments, due dates, sleep cycles, freelance rates – and build the calculator for it 😎

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