Nice project. One thing you'll run into if you keep going: a fixed basket overstates how much your costs rose, because in real life you substitute. When coffee got expensive, did you keep buying the same coffee? Official indices try to account for that, with mixed success.

I didn't, and that's a fair point. I switched brands in March. The index keeps the old one for continuity, so it measures what my habits from last August would cost now, which is a slightly different question from what I'm actually spending. I track both, and the second number is lower.

That's the right way to do it. Most people who try this only track one, then argue with the official figure about the wrong thing.