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AI Context Window Calculator

Estimate how much room an AI request has left after prompt, memory, retrieved context, and reserved response tokens.

App view

Inputs

Model limitsChoose a preset or enter your own
Token budgetBreak down the planned request
Results update automatically

Results

Result Enter values to calculate.
Your result explanation will appear here.

Useful next checks

  • Check the inputs before relying on the result.
  • Try a second scenario to compare outcomes.
  • Read the guide below for context.

# AI Context Window Calculator

Use this calculator to check whether a planned AI request fits inside a model context window. It adds system or developer instructions, the current prompt, chat history, retrieved context, and reserved output tokens.

How It Works

The calculator uses:

  • Input tokens = system prompt + current prompt + chat history + retrieved context
  • Total planned tokens = input tokens + reserved output tokens
  • Remaining context = model context window - total planned tokens

If the remaining context is negative, the request is too large for the selected model limit.

Why Context Windows Matter

An AI model can only attend to a limited number of tokens at once. Long prompts, chat history, uploaded document extracts, and retrieval results all compete for the same window as the answer. Reserving output tokens is important because a prompt that technically fits may leave too little space for the model to respond.

Example

If a model has a 200,000 token context window and your request uses 20,000 input tokens with 4,000 reserved output tokens, the planned total is 24,000 tokens. That leaves 176,000 tokens of spare context.

Limitations

These are planning estimates. Model limits can vary by model version, API setting, beta feature, account, and region. Use provider documentation and actual API errors for production limits.

Related Calculators

Frequently asked questions

Does the context window include the answer?

Yes. The usable context budget includes the input tokens plus the output tokens you reserve for the model response.

Are these exact context limits?

They are static presets for planning. Providers may expose different limits by model version, beta feature, region, or account.

What if I only know words or characters?

Use the AI Token & Cost Calculator first to get a rough token estimate, then bring that number here.