Which SaaS metric did you measure wrong without noticing?

Calculating SaaS metrics is my weekend hobby, same as our family budget and the mortgage plan, which is a strange thing to admit. My conclusion so far: almost every number I report has a definition I can move, and the flattering one always survives.

Nobody lies. The definition just drifts.

MRR: annual contracts divided by twelve, correct, and setup fees in the same total, not correct. Nobody decided that, both arrive as money in the same month.

LTV over CAC is the one that cost me something. Both inputs were already soft and I was treating the result as a decision. A wrong ratio does not look wrong, it is a normal number in a normal range.

So which one did you measure wrong? Not on purpose for a deck. The one where you found out later the definition had moved. 🤔