API vs Subscription Calculator

The break-even is the whole decision

Pay-as-you-go API and a flat subscription are two lines on a graph. The API line starts at zero and rises with every prompt you send. The subscription line is flat - the same price whether you send one prompt or ten thousand. Wherever those two lines cross is your break-even point, and it is the only number that actually decides the question. Below the crossover, the API is cheaper because you are not sending enough volume to justify a flat fee. Above it, the subscription is cheaper because the flat fee has become an all-you-can-eat deal. The calculator above finds that exact crossover for your model and prompt size and tells you which side of it you are on.

The inputs are the honest ones: which model you use, how many prompts you send, how big each prompt is, and how much of your context is served from cache. From those it computes a real cost-per-prompt, multiplies by your volume to get monthly API cost, and divides the subscription price by the cost-per-prompt to find how many prompts it takes to break even.

How API cost is actually computed

• Input tokens - what you send. Billed per million at the model's input rate. Snapshot rates: Opus around 15, Sonnet around 3, Haiku around 0.8 per million. Confirm live.
• Cached input - repeated context is billed at roughly 10% of the standard input rate. A healthy cache hit rate meaningfully lowers your per-prompt cost.
• Output tokens - what you get back. Billed per million at the output rate, which is roughly 5x the input rate. Snapshot: Opus around 75, Sonnet around 15, Haiku around 4 per million.
• Cost per prompt - input plus cached input plus output, summed. Multiply by prompts per month and you have your API bill. That is the entire model.

When the API wins

The API is cheaper below the crossover, which means it wins for lighter or spikier usage. If you use Claude Code a few times a day, or your usage is unpredictable - heavy some weeks, quiet others - metered billing charges you only for what you consume and nothing on the quiet weeks. It also wins when your prompts are small and cheap: tight input, short output, and a good cache hit rate all push your per-prompt cost down, which raises the break-even and keeps you on the API side of it longer. The tradeoff is that metered spend is unbounded, so a spend cap is not optional.

When the subscription wins

The subscription is cheaper above the crossover, which means it wins for heavy, steady usage. If you send hundreds of prompts a day, every day, the flat fee stops being a fee and starts being a bulk discount - past a certain volume you would pay far more per token on the API. The subscription also wins on peace of mind. A flat monthly cost removes the per-prompt anxiety that quietly makes metered users ration their own usage. For daily, interactive work, that psychological unbounding is worth real money in output you would otherwise have skipped.

Why cache hit rate shifts the answer

Cache hit rate is the sleeper variable in this comparison. Because cached input is billed at roughly a tenth of the standard rate, raising your cache hit rate directly lowers your cost per prompt - which raises the break-even and can flip the recommendation from subscription to API. If your sessions reference the same files in the same order and land a healthy 40-50% cache rate, your API cost can be dramatically lower than a naive estimate suggests. If your sessions thrash and hit 0%, the API gets expensive fast. Model your real cache behavior, not a hopeful one.

How to use the break-even in practice

1. Estimate your real prompts per day honestly - count a typical working day, not your busiest one.
2. Read the break-even the calculator gives you in prompts per day. That is your decision threshold.
3. If you are comfortably below it, choose the API and set a spend cap. If you are comfortably above it, choose the subscription.
4. If you are close to the crossover, favor the subscription - the peace of mind and the protection against a heavy month usually win a near-tie.
5. Confirm both numbers on Anthropic's site: the live API rates and the actual subscription price. This tool uses rounded snapshots and cannot know the current figures.
6. Re-run this any time you change your default model or your usage shape shifts materially.

What this calculator does not model

This is a first-order comparison. It does not model tool-call outputs that can spike a single prompt, MCP-loaded context, long-context pricing tiers, per-seat team subscription structures, or the exact terms of any specific plan. It assumes consistent prompt size and average cache behavior. Treat the crossover as a strong planning anchor, then verify against your real dashboard usage over a month before locking in. The goal is to get you on the right side of the break-even, not to predict your bill to the cent.