How this calculator works
Enter model context limit (tokens), prompt and history tokens, reserved output tokens. Select Calculate to apply the displayed formula and review the labeled results.
Formula / method
Remaining input capacity = context limit − prompt tokens − reserved output tokens
Worked example
A 128,000-token context with 48,000 prompt tokens and 8,000 reserved output tokens leaves 72,000 tokens.
Assumptions and limitations
The model’s published context limit includes the entered prompt, conversation history and reserved output.
Providers may count tool calls, images, reasoning or system instructions differently; use the provider tokenizer for exact counts.