Fee Estimation

The Vault estimates the network fee for a withdrawal before it is submitted, so you can show the cost to a user or check it against a budget. Estimation is available in the dashboard and via the API.

Fee Estimation API

Fee estimates are available programmatically: the request identifies the wallet, asset, destination, and amount, and the response returns a single estimate (fee in the native fee currency plus a USD figure). See the Transfers API reference for the endpoint and request/response shapes.

The estimate is a point-in-time figure derived from the node at request time. The actual fee is recomputed when the transfer is broadcast, so the fee paid can differ if network conditions change in between. The definitive fee is recorded on the confirmed transfer.

Network-Specific Fee Models

Ethereum

Ethereum withdrawals are built as legacy (type-0) transactions. The fee is gasLimit × gasPrice, where the gas price is read from the node (eth_gasPrice) at build time with headroom applied. Native ETH transfers use the standard fixed gas; ERC-20 transfers estimate gas from the token contract via eth_estimateGas.

Bitcoin

Bitcoin fees are denominated in satoshis per virtual byte (sat/vByte): fee = feeRate × txVBytes. The fee rate comes from the Bitcoin node’s estimatesmartfee RPC (with a sat/vByte floor). Virtual size grows with the number of selected UTXOs — each P2WPKH input is ~68 vBytes, each output ~31 vBytes, plus ~11 vBytes overhead.

Fee Pricing Source

Fee data is read from each chain’s configured node (Ethereum eth_gasPrice, Bitcoin estimatesmartfee, TRON chain parameters). Sources are configurable per network during deployment.

The API accepts a priority value (SLOW, STANDARD, FAST) on the fee-estimate and transfer requests. It is reserved for future per-tier pricing; the current implementation returns a single node-derived estimate regardless of the value.