RendaFii is a mobile app that I developed in October 2018. It is available in Google Play and App Store. It helps people who invest in Fundos de Investimento Imobiliário (FII) (Brazilian real estate investment funds) know how much and when they will receive their proceeds.

As of March 2023, it has 100K+ downloads, over 30K people use it every month, and it generates a revenue of $150+ per month.

The idea

I developed this app during my spare time the year after I graduated. It was my first year working as a Software Engineer. Back then, I was saving some money and I decided that investing in FIIs would be a good idea.

To invest in FIIs, you first need to buy shares in the stock market. Then, every month, you receive money in your account proportionally to the amount of shares you own. There are several FIIs in the market and each one of them has its own characteristics, risks, dividend yield, etc.

As a young and new investor, I used to check my investments too often. So, I was always on the lookout for when a stock would disclose how much it would pay in the month.

The problem is that I had several FIIs in my wallet, and doing this for each FII was boring. This is how I get the idea of building an app where you could enter the FIIs you have and the app would show when and how much each FII would pay. Simple, huh?

The first release

Although I have abandoned many side projects before, I stuck with RendaFII. This probably happened because it was a real problem for me and I had a good idea of what needed to be done. I remember sketching all the app flows and the necessary screens in Sketch. After I defined the flows, the implementation didn’t took a lot of time.

On October 23, 2018, the first version of RendaFII was published to Google Play. The app was made using React Native and the back-end was a REST API implemented in Python and hosted in Heroku. I used MongoDB as database.

At that time, I thought that the app was too simple and only a few people would consider it useful. Getting more than 100 downloads would already be awesome.

Version 2.0

But its audience started to grow and two months after the initial launch there was more than 2K users per day. So, I decided that I wanted to improve the app. So, I invited my girlfriend, who is now my wife, to help me in this task. She is a designer but she wasn’t working directly with UI/UX at that time. With her help, RendaFII gained a more intuitive and professional look.

In this new version, I also added the PRO Mode. The app was already generating revenue through Ads but I wanted to explore other ways to earn money. So, I started selling a PRO Mode as an In-App Purchase that users could buy if they wanted to remove all Ads from the app.

My first thought was that no one would buy it. The only Ad that existed in the app was a banner at the top of the screen. Who would pay to remove it? But I learned that some people pay and I am thankful to them. I have 25+ purchases a month.

On April 6, 2019, the second version of RendaFII was published. In addition to the new look and the PRO Mode, the app was rewritten in TypeScript, the back-end was now using NodeJS, and it started using GraphQL.

Final words

Since version 2.0, I did a lot of other changes. I migrated the back-end from NodeJS to Clojure, I rewrote the app in Flutter, and I released an iOS version. The app is now in its 4.x version.

I was lucky that when I first developed this app, I was the only one in Google Play. There weren’t many FII investors in Brazil and, because of that, there wasn’t an app for that. A few years later, the number of FII investors started to grow very rapidly and now I have several competitors.

For a long time, RendaFII ran without any cost. The back-end has always been hosted in Heroku. For years, it used Free Dynos, and I only migrated from them in 2022 when Heroku stopped offering them. The Free Tier offered by MongoDB (ex-Atlas), Amplitude, Firebase, and Sentry were always enough for RendaFII’s volume.

So, for about 5 years, I had an app generating income of ~$150 a month without any expenses. Today, I pay $5 per month to Heroku.

RendaFII helped me a lot in my journey as a Software Engineer and I am very proud of it. It helped me in job interviews, and it was also the playground where I tested and learned a lot of new technologies.

Finally, I am very glad that I could make people’s lives a little bit easier by implementing RendaFII. I know it is a very very very small problem but it makes me happy nevertheless.