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Designing a Personal Subscription System

February 2026

Subscriptions are invisible systems that quietly shape our spending. I wanted to make them measurable. By connecting APIs and modeling usage against cost, I built a personal feedback loop that calculates real value per minute. This project applies product thinking to everyday life.

Zwift

The Zwift subscription costs €19.99 per month.

No activities this month

Simple Idea

It is quite simple. I wanted to find out what my subscriptions actually cost me and how those costs relate to my real usage. This year I want to live with less and only pay for what I truly need. In the end it has to be worth it for a subscription to stay. The question is: how can I track this properly and does it even make sense?

System Thinking Instead of Spreadsheets

Without APIs it becomes difficult. Of course I could calculate everything in Excel, but that would be boring and not very exciting. So let's start. I will begin with the simplest case. Cursor, Codex and ChatGPT are my helpers. Since Zwift does not provide accessible usage data, I have to go through Strava.

Easy Prompt, Easy Life.

I want to track my Zwift costs through Strava. My goal is to use the Strava API to collect all indoor and virtual ride activities on a monthly basis. The subscription costs 19.99 euros per month. The costs of the trainer and the bike itself are not included.

Next Steps

  • Use Literal API and calculate all books I read through Kindle unlimited.
  • Netflix and similar services will be more difficult. There is no direct API, so this will probably require a hybrid approach with an external provider.
  • Apple Music unfortunately does not allow proper tracking through Last.fm. I need to find another solution. With Spotify this would be easier.
  • Runna for running should be simple via Strava.
  • It would also be interesting to calculate what a single image in iCloud actually costs.
  • Audible listening minutes are another metric I want to explore.

Next Next Steps

  • Create a complete overview across all subscriptions.
  • Set up an automatic reminder when my costs increase but my usage decreases.
  • Automatically pause subscriptions when I am clearly overpaying.