Your LLM bill has two sides. Build the ledger that shows both.

Every RAG cost estimate starts the same way: input tokens equal top_k times chunk size, plus some overhead. Most of them stop there too. Then the invoice arrives, it is three times the estimate, and the team spends a sprint tuning chunk sizes while the actual money leaks somewhere that formula never touches. The bill for an LLM system is set by total input and output tokens, summed across every call a query triggers. Not per call. Not input only. Every call, both directions. If you only…