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How the math works
Three plain cost models, computed live above:
- Buy, the hardware price upfront, plus electricity: TDP × a 0.7 typical-load factor × your active hours × your $/kWh. Hardware prices come from our tracked data layer, with used gear labeled as such.
- Rent, a cloud GPU by the hour (RunPod, Vast.ai and similar; the default rate is a typical RTX-4090-class community price, check current rates, they move weekly).
- API, pay per token. Enter a blended (input+output) price per million tokens for the model class you'd use.
The break-even months are simply: hardware price ÷ (what you'd pay monthly the other way − your electricity). Dots on the chart mark them.
What the calculator deliberately ignores
For the record: resale value (used hardware holds value well, which favors buying more than these curves show), cloud spot-price swings, API price cuts (historically frequent, long-horizon API totals are probably overestimates), and most importantly everything that isn't money: privacy, working offline, latency, no rate limits, and the simple joy of owning the machine. Plenty of people run local AI knowing it costs more than an API. That's a feature, not an error.
Use it with the fit calculator
This page answers "should I buy at all?" Its sibling, Can I run it?, answers "what exactly can the hardware run?", model sizes, quantization, context length, and which machines fit. Between the two you can go from curiosity to a defensible purchase decision without leaving the site.
Disclosure: hardware links and the cloud-GPU links on this page are affiliate/referral links (details). They never change the math.