What this calculator answers

Once you understand that input tokens cost money on every API call, the next question is how much you could save by shortening your prompts. The Prompt Token Reducer estimates the dollar impact of compressing your system prompt or context window, given your monthly call volume and pricing tier. It often surfaces savings of hundreds or thousands of dollars a month from changes that take an afternoon to ship.

How the math works

Take your current average input token count, multiply by monthly request volume, multiply by the per-million input price, and you have your baseline input spend. Reduce the token count by your target percentage (say 30 percent) and recompute. The difference is the monthly savings. Output savings are usually smaller because output length is driven by user need, not prompt length.

When to use it

• Your monthly API bill has crossed a threshold (often 1,000 dollars a month) and leadership is asking for cost cuts.
• You are preparing to scale a feature 5x or 10x and want to bring per-call cost down before traffic ramps.
• You have a long system prompt accumulated from months of patches and want to know whether a rewrite is worth the engineering time.
• You are evaluating whether to invest in prompt caching, prompt compression, or model swapping as the highest-leverage cost reduction.

Common mistakes

• Reducing tokens at the expense of output quality. A 30 percent token reduction that drops accuracy by 5 percent is usually not worth it.
• Counting words instead of tokens. The OpenAI tokenizer (cl100k) treats 'the' as one token and 'antiestablishment' as multiple tokens. Always use a tokenizer for accurate counts.
• Optimizing the user prompt instead of the system prompt. The system prompt is sent on every single call and is usually the largest fixed cost.
• Ignoring the engineering cost of the reduction. Spending two engineer-weeks to save 200 dollars a month has a poor payback period.

A worked example

Your application makes 100,000 API calls per month with an average input length of 2,400 tokens at 3 dollars per million input. Current monthly input cost is 720 dollars. A 35 percent reduction in average input length (to 1,560 tokens) drops the monthly input cost to 468 dollars, saving 252 dollars per month or about 3,024 dollars per year. If the reduction took 20 hours of engineering work, the payback period is roughly four months.

Frequently asked questions