LLM Context Window Calculator
See what fits before a huge prompt fails or gets truncated.
Free · no signup · runs in your browserWhat this calculator is for
Context is shared by system instructions, conversation history, documents, tool definitions and the model response. This calculator provides a quick heuristic before you use an exact tokenizer.
The math
Actual invoices can differ because providers may apply long-context pricing, caching rules, batch rates, tool-call fees, regional processing, negotiated contracts, taxes, or future pricing changes. Treat the output as a planning estimate.
Pricing sources
Current model rates are sourced from official provider pricing pages and verified on August 28, 2026. The methodology page records the source links and known limitations.
Frequently asked question
Is this an exact token counter?
No. It is a browser-side heuristic. Tokenization varies by model and language; use a provider tokenizer for billing-grade counts.
Can I use this estimate for a production budget?
Use it to create scenarios and catch order-of-magnitude mistakes. Before committing spend, verify the selected model's live provider pricing and compare the estimate with actual usage telemetry.