How to Calculate AI API Cost
What is AI API Cost?
An AI API cost calculator estimates the cost of using large language model APIs based on token usage. AI APIs charge separately for input (prompt) and output (completion) tokens.
Formula
cost = (input_tokens × rate_in) + (output_tokens × rate_out)
- T_in
- Input tokens (tokens) — Tokens sent to API
- T_out
- Output tokens (tokens) — Tokens generated by API
- rate_in
- Input rate ($/1M tokens) — Price per million input tokens
- rate_out
- Output rate ($/1M tokens) — Price per million output tokens
Step-by-Step Guide
- 1Cost = (input tokens ÷ 1000) × input rate + (output tokens ÷ 1000) × output rate
- 2Rates are per 1,000 tokens (or per million tokens on newer models)
- 3Monthly cost = cost per request × monthly request volume
- 4Input tokens are typically cheaper than output tokens
Worked Examples
Input
GPT-4o: 500 input + 200 output tokens, 1000 req/month
Result
~$3.25/month
Input
Claude Haiku: same usage
Result
~$1.20/month
Input
GPT-4o-mini: 1M requests/month
Result
~$150–300/month typical
Frequently Asked Questions
Why is output more expensive than input?
Generating tokens is computationally more costly than reading them. Output pricing reflects the higher compute cost.
How do I estimate total API costs?
Calculate (input tokens ÷ 1,000,000) × rate_in + (output tokens ÷ 1,000,000) × rate_out. Track all API calls.
What are typical LLM token rates?
As of 2026, rates vary: Claude 3.5 Sonnet ~$3/$15 per 1M tokens; GPT-4 ~$30/$60; open-source may be cheaper.
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