kcalculator.de: How Jannis Kuhrt Builds B2B SaaS Alongside Full-Time Job and Family
"Happy Bootstrapping" Volume #41
Jannis Kuhrt is 36 years old, innovation team lead in corporate, father of two daughters – and building kcalculator.de on the side. A B2B SaaS solution for nutrition professionals.
But before that, Jannis built kids beds for seven years and sold low-carb muesli. Two businesses that worked – but failed on margins. A story about three startups, the realization “input-to-output ratio is too low,” and why digital products win.
This is a summary of Episode 153 of the “Happy Bootstrapping” Podcast (German).
Startup #1: Kids Beds – From Instagram to Nina Bott
Jannis started with kids beds after university. “I wanted to buy a kids bed for my daughter – a play bed with a roof. I thought: I can build that myself.” Half a year later, the bed was finished. He posted it on Instagram. Ten people asked where they could buy it.
“I took the hourly rate from my corporate job, calculated how long I’d need, and offered a price. Five bought it.” A great feeling: people invest their most important resources – time and money – in your product.
The business ran well. A parenting magazine featured a permanent page. Then Nina Bott’s management (TV host) wrote: “Nina would like your bed and would do advertising.” Revenue increased.
But after seven years: “Dirty, heavy, raw material prices increased, shipping limits raised.” In the end, everyone earned more than Jannis – shipping companies, taxes, suppliers. “That really annoys me.” He still has wood left: “I still have wood for kids beds in the garage that I occasionally chop up for the fireplace.”
Startup #2: Lüsli – Low-Carb Muesli with Margin Problem
After the kids beds, Jannis focused on nutrition and sports. He built a low-carb muesli – inspired by Lizza. “I realized there’s nothing on the market that I like.” Friends and family found it delicious. So he built a business.
450 grams for almost 15 euros – a high-price product. “Still, the margins were very low.” The food retail sector wasn’t digitalized. “You have to call stores, wait five minutes, then the boss says: We still have five packages, send five more. That doesn’t scale.”
Friends with a food startup in 300 Edeka stores shut down. “Too many regulations, best-before dates, input-to-output ratio very low.” Jannis completed a nutrition consultant certification during this time – and found his next problem.
Startup #3: kcalculator.de – B2B SaaS for Nutrition Professionals
“I realized nutrition professionals have a problem: They spend too much time on administration instead of with their clients.” Jannis built kcalculator.de – a B2B SaaS solution that supports nutrition professionals with meal plans, consulting, and administration.
The tech stack: Vue.js frontend, Capacitor for mobile, Bun + Elijah.js for APIs, Firebase backend, TypeSense search, hosted on Hetzner VPS in Germany. All as a side project alongside full-time job and family.
The special part: Jannis learned from his previous failures. Hardware and food? Margins get eaten up. Digital? Scalable. “Software as a Service” – or better: “Service as a Software,” as he says. The focus is on output orientation, not just software.
The AI Question: Competition or Opportunity?
Will AI replace nutrition consultants? Jannis sees it pragmatically: “The main issue with nutrition isn’t knowledge, but the coaching aspect. Very few people fail to lose weight because they don’t know they should eat less.”
Google AI answers lead to 30-40% search volume drops on main keywords. “Sure, many will use AI. But nutrition professionals will continue to exist because you need that therapeutic aspect.”
His strategy: Adapt AI where it makes sense. “Many launch tools just because they can. Then they wonder why they can’t monetize it. We don’t just throw AI in because it’s possible.”
Bootstrapping on the Side: How Does That Work with Two Kids?
Jannis works full-time, has two daughters (11 and 4), and builds kcalculator.de. How? “Sports – road cycling in summer, running. And time with kids forces you to disconnect.”
“When a child says: I want to build this picture now – that’s the most important thing for them in that moment. In their world. If you can engage with that, it brings you down massively.”
Jannis even wrote a book about bootstrapping on the side (available also on Kindle Unlimited). His vision for 2026: Version 3 of kcalculator.de with better AI integration. “When you throw cool people in a room who work on something they’re passionate about, something great always comes out.”
What I Learned from the Interview:
Hardware/food eat margins: Shipping, taxes, raw materials – in the end everyone earns more than you. Digital scales better.
Input-output ratio is decisive: When effort exceeds output, it’s time to move on.
Service as a Software > Software as a Service: Customer output counts, not just the tool.
Learnings for Founders:
Learn from failures: Jannis shut down two businesses – and built a better third from them.
Digital products scale: No raw materials, no shipping, no best-before dates.
Side projects work: Alongside full-time job and family. Sports and kid-time help disconnect.
Adapt AI, don’t blindly integrate: Just because you can doesn’t mean you should.
Bootstrap on the side: Jannis wrote a book about it. No risk, but slow growth.
Happy Bootstrapping is a German podcast where I interview bootstrapped founders, indie hackers, and solopreneurs about their startup journeys.
Over the years, I’ve connected with many successful entrepreneurs who have built e-commerce shops, SaaS platforms, mobile apps, content businesses, or hybrid models.
Furthermore I am a bootstrapper myself and growing my DevOps-as-a-Sercice and Web Operations Company “We Manage”.
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