Context overflow cost calculator
When a prompt is too large for the model’s context window, you have to do something before the API will accept it. The two common fixes — truncating the oldest tokens or summarizing them into a shorter form — have very different cost profiles. This calculator models both across a month of traffic so you can pick the cheaper strategy for your actual overflow rate.
How it works
Each overflowing request costs you in one of two ways. Truncation is free in dollars but carries a hidden quality cost: some share of those requests produce a worse answer because needed context was dropped. Summarization avoids the quality hit but adds a real token cost — you run an extra compression call on every overflow.
overflows/month = monthly_requests × overflow_frequency
summarize_cost = overflows/month × cost_per_summary
truncate_quality = overflows/month × quality_loss_rate (requests degraded)The tool shows the monthly dollar cost of summarization and the monthly count of degraded requests from truncation, so you can weigh cash against quality.
Tips and notes
- Measure your real overflow rate first. Log how often prompts hit the window. Many teams over-engineer for overflow that happens on under 1% of calls.
- Hybrid wins at scale. Truncate cheap, low-stakes requests and reserve summarization for high-value ones where a wrong answer is costly.
- Right-size the window. Moving to a larger-context model can be cheaper than paying for summarization on every overflow — compare both.