System Prompt Cost Calculator
See what a fixed system prompt costs at scale.
With the default inputs, $300.00/month — Your 800 tokens system prompt, sent every request. Enter your own numbers below to recompute instantly; the full step-by-step math is shown under the worked example.
Results update automatically as you type.
- System prompt tokens
- 800 tokens
- Cost per request
- $0.00100
- Cost per month
- $300.00
A system prompt is re-sent on every request, so a long one quietly adds up. Enter its size and your volume to see the monthly cost, and how caching changes it.
How this is calculated
Monthly cost = system prompt tokens × requests per day × 30 × input price, because the system prompt is re-sent on every request. If you set a cached share, we bill that portion at roughly 10% of the input rate and subtract the saving.
Is this a good result? What to do next
A long system prompt feels like a one-time write, but it's billed on every call — so at high volume it becomes a real line item. If it's a meaningful share of your bill, caching a stable prompt cuts about 90% of its cost.
Typical planning ranges
- System prompt
- re-sent on every request
- Cached
- ~10% of the input rate
- Impact
- grows linearly with volume
Ranges are typical planning figures to sanity-check your result, not authoritative benchmarks. Your numbers will vary with use case, volume, and vendor.
How to improve this number
- Trim to the minimum prompt that stays reliable.
- Cache the stable prefix where supported.
- Move few-shot examples out into a separate, cacheable block.
Common mistakes
- Treating the system prompt as free because it's written once.
- Leaving a long prompt uncached at high volume.
When to use a different approach
For the full caching math, use the prompt caching savings calculator. For examples specifically, use the few-shot prompt cost calculator.
Worked example (defaults)
With the default inputs above, here is the result:
- System prompt tokens
- 800 tokens
- Cost per request
- $0.00100
- Cost per month
- $300.00
- A fixed system prompt is re-sent on every call; caching cuts this sharply.
Sources & references
Frequently asked questions
Should I cache my system prompt?+
Yes, if your provider supports it and the prompt is stable. Caching a long system prompt can cut its cost by ~90%.
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