I found a tool that estimates LLM API costs before you send the request

Ryan — Thu, 16 Apr 2026 01:57:38 +0000

Got hit with a $212 API charge from Claude Opus last month. Completely my fault, I wasn't paying attention and didn't set a hard limit. What shocked me wasn't just the amount, it was how fast it happened. A small side project, a few hours of testing, and suddenly a $212 invoice.
After doing some research I figured out what happened. Every message in a multi-turn conversation sends the entire conversation history along with it. So by turn 10 or 15, even a short message is actually sending thousands of tokens. What felt like a quick test session was compounding the whole time. The billing dashboard just shows one line, total usage, with no breakdown of which requests cost what.
I went looking for something that could estimate costs before sending anything. Most of what I found were basic calculators where you manually enter token counts and get a price. Useful but limited, they only count input tokens, and the response is usually where most of the bill comes from. Nobody seems to have solved output token prediction before generation.
Then I found Calcis. You paste a prompt, pick a model, and it estimates the full cost before you send anything. The output prediction is what makes it different from every other calculator I tried.
I only explored it a bit before hitting the usage limit on the free tier, but what I saw worked well. Supports many models across OpenAI, Anthropic, and Google. There's also a conversation modeler that simulates how costs compound across multiple turns, which would have saved me that $212 if I had it earlier.
Basic estimator is free with no account needed. Some features are behind a paywall but the core tool does what it says.
calcis.dev if anyone wants to try it.

DEV Community: Ryan

I found a tool that estimates LLM API costs before you send the request