I built my first iOS app in 2.5 months while working full-time at Google — mostly because I didn’t want to pay £240 a month for a personal trainer

A few months ago I started going to the gym again after a long period of being inconsistent.

I’ve done the gym thing before, but like many people I would start strong, skip a few sessions, lose momentum, and eventually stop. This time I wanted to do it properly, so I looked into getting a personal trainer at my local gym in London.

The price was £240 per month for four sessions.

What surprised me wasn’t even the price itself — it was what the service actually included.

The trainer asked a few questions about my goals, experience level, and schedule. Then they created a workout plan: exercises, sets, reps, and progression. We would meet once a week in person, and the rest of the time I was just logging workouts in their app while following the plan they created.

During one of the sessions something interesting happened.

While I was training, a lot of younger guys in the gym kept coming up to the trainer asking really simple questions:

“Am I doing this bench press correctly?”

“Is this weight too heavy?”

“How many sets should I do?”

You could also see beginners making classic mistakes everywhere — skinny guys lifting way too heavy, people doing endless curls, terrible form on compound lifts.

At that moment I had a pretty simple thought:

Why is this knowledge so expensive and inaccessible when most of it is structured and repeatable?

A workout plan is basically a system.

Track your progress.

Increase weights gradually.

Adjust based on your experience and goals.

That’s when the idea started forming: what if an app could do the same thing a beginner personal trainer does — but cheaper and accessible to everyone?

The hackathon that started it

Around that time there was a hackathon, and I mentioned the idea to a friend of mine. We both work in tech (I’m an SRE in Google Cloud in London, he’s also in big tech), so we decided to try building it.

Neither of us had ever built a mobile app before.

Zero mobile development experience.

No React Native experience.

No real UI/UX design background.

But we had two advantages:

1. We understood software architecture and systems
2. AI tools made it possible to move extremely fast

So we decided to try.

The 2.5 month sprint

We started building around November and launched the app around February.

The entire journey took roughly 2.5 months.

It was chaotic.

Working full-time in a big tech company already comes with a lot of cognitive load, and this became a late-night / weekend project.

There were weeks where the routine looked like this:

Work → Gym → Fix bugs → Sleep → Repeat.

The funny part is that I was one of the main users of the app while building it.

I’d go to the gym.

Log my workout.

Notice something annoying or broken.

Then I’d go home and fix it.

Next gym session — new bug discovered.

Fix it again.

That loop happened dozens of times.

Our first real users

We started distributing the app through TestFlight and invited around 30 testers — mostly friends and relatives.

They were incredibly helpful.

People would send screenshots, complaints, suggestions like:

• “This button is confusing”

• “I don’t understand this screen”

• “Can you add this exercise?”

• “The timer should behave like this”

We iterated constantly.

UI/UX was probably the hardest part for me personally. Engineers often underestimate how hard it is to design something that feels simple.

You quickly realize that fitting multiple features into a small mobile screen without overwhelming the user is very difficult.

We redesigned screens many times.

The engineering approach

Even though this was an MVP, we tried to build it in a way that wouldn’t collapse later.

We used:

• React Native for the mobile app

• AI tools heavily for development

• A fairly simple but scalable backend structure

Interestingly, our workflow was very different from the traditional Git flow.

Because we were essentially operating like a 24/7 relay team, we didn’t do long feature branches or complex merges.

Instead it looked like this:

• I code → push to main

• He wakes up → pulls → continues → pushes

• I wake up → pull → continue

It was basically continuous development across time zones.

During the holidays this got even more chaotic because sometimes I was on vacation while he was working, and vice versa.

But somehow it worked.

App Store reality

One thing nobody tells you about launching an app:

The App Store review process can be brutal.

We got rejected multiple times for different reasons:

• authentication configuration issues

• policy misunderstandings

• UI problems

Each rejection meant another fix, another submission, another wait.

I also had to learn things I had never touched before:

• Apple developer policies

• authentication branding requirements

• setting up proper web pages for OAuth

• dealing with app metadata and compliance

It was a lot of small things you only discover when you actually try shipping a product.

Launch day

Eventually the app was approved and GymBro AI went live on the App Store.

The core idea is simple:

You enter your:

• gender

• age

• experience level

• available equipment

• how many days you want to train

The app generates a workout plan and then lets you track progress and progressively increase weights over time.

Nothing revolutionary.

But the goal was always simple:

Make something cheap, accessible, and easy to start with for beginners who don’t want to spend hundreds on coaching.

What I learned

This project taught me more than I expected.

A few takeaways:

1. Building something is very different from thinking about it

You only discover real problems when you start shipping.

2. UI/UX is much harder than backend systems

Good interfaces take a lot of iteration.

3. AI dramatically accelerates development

Without AI tools this probably would have taken us 6–8 months instead of 2.5.

4. Being your own user is incredibly powerful

Many of our improvements came from using the app ourselves daily.

5. Shipping is the hardest part

Getting from idea → App Store approval is a journey full of unexpected obstacles.

I’m not sure where the project will go from here yet.

But launching something real — especially something people actually use — was a very different experience from building internal systems at a big company.

If anyone here has gone through a similar first app / first startup / first side project launch, I’d love to hear your stories.

And if you’re thinking about building something — honestly just start.

The hardest step is usually the first one.

If you want to support us and try our app, here’s the link. Tell us what you think.

App Store