How to Set Minimum Output for Cross-Chain Swaps

A minimum-output setting defines the least destination asset a cross-chain swap can deliver before the protocol refuses execution or returns the input. Set it from a current quote, with the destination chain’s fees and the cost of a refund in view.

The threshold is the price boundary on your trade: a tighter one protects the quoted value more closely, but makes a failed or partial execution more likely.

The key distinction is between expected output and minimum output. Expected output is an estimate based on current pool state; minimum output is the floor your transaction accepts. On THORChain, for example, swaps between assets other than RUNE pass through two pools, and the pool balances can change before execution. The thor swap account traces that route in more detail. For setting a floor, the practical task is to translate the quoted result into an amount you can accept after the swap’s applicable fees.

How do you calculate a minimum output?

Start with the quote’s expected amount out, then apply a tolerance for adverse price movement. If the quote predicts 2 units and your tolerance is 1%, the floor is 1.98 units, assuming the interface applies that tolerance to the quoted destination amount. Use the value and units the swap interface or memo expects; token precision varies, and a raw integer may represent the smallest denomination rather than a whole token.

Check how the quote treats costs. Some quote systems include swap and outbound fees in expected output; others calculate a price tolerance from the input value and can produce a floor that does not account for those fees. Prefer a fee-inclusive minimum when the interface provides one. Otherwise, reconcile the quoted output, network fees, affiliate fees if any, and the amount that will actually reach the destination address before confirming.

What happens when the swap misses the floor?

That depends on the swap mechanism. A one-shot swap with a minimum-output condition generally executes only if it meets the limit; otherwise it fails or is refunded. In THORChain streaming swaps, the limit can apply to each sub-swap: attempts that miss the price condition may be refunded while successful portions proceed. The result can therefore be a partial swap plus a return of the unexecuted source asset, rather than one all-or-nothing destination amount.

A refund is not necessarily cost-free. Cross-chain protocols may charge a source-chain outbound fee to return assets, and network fees can change. Before sending, confirm the refund address, the quote’s expiry, and whether the interface describes the limit as a total-output floor, a per-step price condition, or a trade target. These settings govern different points in execution.

How tight should the minimum be?

Choose the tightest floor that still reflects a realistic execution range for the route and the time you are willing to wait. A loose floor allows greater price movement and improves the chance of completion, but it also accepts a worse result. A strict floor rejects more movement, but can leave funds waiting or trigger a refund if the market or pool balances shift before execution.

• Refresh the quote immediately before sending, especially after a delay or material price move.
• Compare expected output with the minimum in the same destination asset and units.
• Check whether fees are already deducted from the quoted amount.
• Read the failure and refund terms, including which chain pays the return transaction.

For most users, the better setting is a fee-aware floor based on a fresh quote and a tolerance they can explain in destination-token terms. Treat the quoted output as an estimate, and the minimum as the actual boundary your transaction authorizes.