Estimate the number of tokens an LLM completion or response will generate.
Completion token estimation helps predict API costs and ensures the model has enough room within the context window for its response. English text averages about 1.33 tokens per word with BPE tokenizers.
Completion Tokens
tokens = expected_words × tokens_per_word
Yes — most APIs have a max_tokens parameter that caps completion length. Setting it prevents runaway generation and controls costs.
With many providers (OpenAI, Anthropic), completion tokens cost 2-4x more per token than input/prompt tokens.