The LLM API Cost Calculator

Know what your prompts and agent runs will cost before the invoice tells you. The LLM API Cost Calculator is a spreadsheet for developers, indie hackers and operators who pay for model APIs by the token. Type in your prompt and output sizes, cache hit rate and volume, and it shows cost per call, per day and per month. For agents, it models the part that usually blows budgets: context that grows with every step, plus tool-call overhead and retries. You get cost per run, per day and per month, with a step-by-step breakdown.

Then put the numbers to work. The Model Comparison tab prices the same workload on every model in your price table and sorts them cheapest first. Budget & Pricing shows how many runs a monthly budget covers and suggests a per-user/seat price at your target gross margin, with a heavy-user check, so you can price an AI product without guessing. The price table comes prefilled with 12 models from OpenAI, Anthropic, Google, xAI and DeepSeek. Each price was copied from the provider's official pricing page and carries its source link and an "as of" date (15 Oct 2026). Prices change, so the table is fully editable and the workbook tells you to check it.

What's included

• LLM-API-Cost-Calculator.xlsx with 6 tabs:
  • Start Here: how to use it, colour key, and what it doesn't model
  • Model Price Table: input / cached input / output price per 1M tokens for 12 models, each with source URL, "as of" date and price notes, plus 8 blank rows for your own models
  • Per-Call Estimator: prompt tokens, output tokens, cache hit %, calls/day → cost per call/day/month (with an optional words-to-tokens helper, clearly labelled as an approximation)
  • Agent Run Estimator: steps, context growth per step, tool-call overhead, retries, caching → cost per run/day/month, plus a 30-step breakdown table
  • Model Comparison: one workload across every model, sorted by cost
  • Budget & Pricing: max runs for a budget, suggested price per user/seat at a target margin, margin sensitivity and a heavy-user check
• Clearly marked input cells, locked formula cells (sheet protection has no password), dropdowns and data validation
• Labelled sample inputs on every tab, ready to overwrite
• Quick-Start-Guide.pdf (4 pages): setup, how each estimate is calculated, a hand-checked worked example, and the price sources

Works in Excel 2010 or later (desktop or web), Google Sheets (via import) and LibreOffice Calc. Estimates only: your provider's invoice is the source of truth.