How this calculator works
The x402 Micropayment Fee Calculator prices the same transaction two ways. The x402 rail costs whatever gas the settlement takes on a low-fee chain like Base, plus an optional protocol or facilitator fee set as a percentage of the transaction value — most facilitators today charge no fee beyond gas, which is why that field defaults to zero. The card processor costs a flat fixed fee plus a percentage of the transaction value, the standard Stripe-style structure. Multiplying each per-transaction cost by your monthly volume gives the two invoices compared at the top.
The crossover transaction size is the value at which the two costs are equal, solved directly from both formulas rather than read off a chart. With a zero protocol fee, x402 wins at every transaction size and the gap widens in dollar terms as transactions get larger, because the card processor's fixed fee never goes away while its percentage keeps compounding. The only way the card processor becomes cheaper at scale is if you set a protocol fee percentage above the card processor's own percentage — in that case a genuine crossover appears, and transactions larger than it are cheaper on cards. That is the honest, non-obvious result: x402's advantage is not automatic at any fee level, it depends on what a given facilitator actually charges. All rates here are adjustable assumptions, not live network data — confirm current gas and facilitator fees before relying on this for a production decision.
Frequently asked questions
What is x402 and how does it work?
x402 revives the long-dormant HTTP 402 "Payment Required" status code as a real payment rail for machines. An API that wants payment responds 402 with the price and accepted asset; the requesting client — typically an AI agent — attaches a signed payment authorization for that exact amount in a stablecoin such as USDC, a facilitator verifies and settles it on a low-fee chain such as Base, and the original request is retried and served, all in under a second with no account signup, no stored card, and no human in the loop. Coinbase published the initial specification and facilitator in 2026 specifically so agents could pay per call for tools and data the same way a browser fetches a webpage.
How much cheaper is x402 than a card processor for AI agent payments?
At typical machine-to-machine transaction sizes — a cent to a few cents per API call — a card processor's roughly thirty-cent fixed fee alone is often larger than the entire payment, which is why per-call card billing for agents essentially does not exist below about ten dollars per transaction (fixed fee divided by the percentage rate is the rough threshold where the fixed fee stops dominating). x402's cost is network gas on a cheap layer-2 chain, typically a hundredth of a cent or less, so it wins by two to four orders of magnitude at these sizes and keeps winning as volume scales, since the underlying rail has no fixed floor per transaction.
Does x402 have any fees at all?
Yes, but they are usually just network gas. Most current x402 facilitators charge nothing beyond the underlying chain's transaction fee, which is why the default protocol fee in this calculator is 0%. Some facilitators or marketplaces built on top of x402 may add a small basis-point fee for verification, settlement guarantees, or dispute handling — the calculator lets you set that fee directly. If it ever grows large enough to exceed a traditional processor's percentage rate, the crossover result above shows the exact transaction size above which card processing becomes cheaper again — the honest answer is that x402's advantage is not automatic at any fee level, it depends on what the facilitator charges.
Is x402 only useful for tiny transactions?
It is most valuable for sub-dollar machine-to-machine payments where card economics break down completely — no per-call authorization flow to build, no thirty-cent floor eating the entire transaction, no chargeback risk on a call that already ran. That said, the same rail settles larger agent-to-agent payments too, and the crossover table above shows how the size of x402's advantage changes as the transaction grows: in dollar terms it widens, and in percentage terms it holds steady near the gap between the processor's rate and whatever protocol fee you set, rather than shrinking to zero.