A few weeks ago I realized I was turning 33.33 years old sometime this year — exactly a third of a century. It got me thinking about what other mathematical or interesting milestones we pass without realizing.

So, I built a small tool to calculate them. You input your birth date, and it generates a timeline of your past and future milestones (like 1 billion seconds, 400 months, or 10,000 days) that you can easily sync to your calendar. I also added a satirical “dark mode” that swaps out the fun milestones for existential dread.

I originally built it as a simple Vite/React app, but I had some issues with getting custom share links with generated Open Graph images to work when you send them to a friend. So, I ended up rewriting the base of the app in Next.js just to get SSR and dynamic Open Graph tags working for the custom share cards.

All the actual date math runs client-side for privacy, and I’m self-hosting it on a VPS using Dokploy. I also added some privacy respecting analytics with Umami to monitor traffic.

I had a lot of fun building this project, especially brainstorming ideas for milestones with my friends (and AI). I would love to get some more ideas for more milestones or new “modes” I can add.