What it costs (theoretically) to run your app – The Startup Day 1

I’m stingy with my money. I want to use it wisely. That’s why creating my own app Fields I made sure to get everything out of the money I spent. Here’s how it goes.

What costs Fields has
The only thing that costs money in Fields is the database, Firebase service called Cloud Firestore. Over there I save all the data users generate: Users, Fields, Teams, Events and Friends. Saving data here is butter smooth and building the app by just simply fetching data from the database every time users need it, would make things 1000x more simple. But this service comes with a price, ~0.10$ per 100k fetches. This really is an awesome pricing, but scaling the app up and these fetches really start compounding.

Fields is currently in the very beginning state of an app, launched on Google Play couple of days back and coming to iOS in couple of weeks, so I don’t have any real world usage data, but here’s how much I calculated the database to cost and how big profit margins I (theoretically) expect and also how exactly I make the app more database-efficient.

Saving database usage
The main fetch-saving method is saving the data to users device and updating it only when required. If user for example opens the field search screen, there is a list of all the nearest fields. Let’s say there’s 20 fields, so every time user opens the screen, 20 fetches are used. Not optimal. What I do instead is save the 20 near fields to users device, and when opening the search screen, 0 fetches are required as everything is coming from the users device. For free.

Implementing this strategy to multiple places across my 30-screen app, I calculated that during users normal day of use the app required around 50 fetches. Divide the free usage quota of Cloud Firestore (90 000 fetches) with 50 and rounding down for more realistic picture (Things usually take more than you calculate) I can expect to sustain ~1000 users daily for free. Without the optimisation this number would have been tenfold smaller.

Again this is all my no-real-world-data assumptions, but I’m eager to see how these play out. I offer a monthly subscription for 3$, after Google/Apple taking their 30% I get 2.1$. Expecting that 1% of Fields’ users have this subscription, I would generate 21$/month without any costs.

After going to the paid side (0.10$ for 100k fetches) i can expect to sustain 2000 daily users for a daily sum of 0.10$, or for 2.58$/month. From 2000 users calculating that 20 users have a subscription, it would generate 42$/month. So 16:1 profit rates. Good in theory, more exciting to see it in real world. Thats why I don’t give too much value for these numbers, but what I can see is that this can be profitable when done right.

Time to get back to Fields, we see tomorrow, — OT, Fields

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