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The Estimate Fee endpoint calculates the expected network fee for a transaction before you submit it. Use this to show fee estimates to end users, validate that a wallet holds sufficient gas, or build fee-inclusive UIs. You supply a fee_rate expressed in the units appropriate for the target blockchain (see the table below), and for UTXO chains you must also supply the amount so the API can calculate transaction size. The response returns the total estimated fee denominated in the blockchain’s native token.

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Fee Rate Units by Blockchain

Different blockchains use different units for their fee rate parameter. Use the table below to determine the correct unit for your fee_rate value.

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Request

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string
required
Your Finrock API key.
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string
required
Your JWT bearer token in the format Bearer {JWT}.
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string
required
The asset for which to estimate the fee. Use the asset_name value from the Supported Assets list (e.g. BTC, ETH, USDT_ETH).
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double
The amount to transfer in the asset’s native unit. Required for UTXO chains (BTC, LTC, DASH, DOGE, BCH) because transaction size — and therefore fee — depends on the number of UTXOs selected to fund the transfer. Optional for non-UTXO chains.
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float
required
The desired fee rate, expressed in the unit appropriate for the target blockchain (see the table above). For example, pass 20 for 20 GWei on an EVM chain, or 10 for 10 Sat/Byte on Bitcoin.

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Example Request

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Response

A successful request returns HTTP 200 with the estimated fee.
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string
The asset for which the fee was estimated.
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number
The estimated network fee, denominated in the blockchain’s native token. For token assets (e.g. USDT_ETH), the fee is returned in ETH, not in USDT.
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number
The fee_rate value used for the estimate, echoed back in the response.
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string
The unit of the fee_rate used (e.g. GWei, Sat/Byte).
Sample 200 Response — ETH
Sample 200 Response — BTC
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object
Returned when the x-api-key or Authorization header is missing or invalid.
Sample 401 Response
Fee estimates are approximate and based on current network conditions at the time of the request. The actual fee deducted when the transaction is confirmed may differ if network congestion changes between the estimate and submission.