estimatesmartfee

estimatesmartfee asks a Bitcoin Core node for the BTC fee rate it expects you will need so a transaction confirms within a target number of blocks. Bitcoin mines a block roughly every ten minutes under Proof-of-Work, and fees are paid in BTC (denominated on the wire as a rate per kilo-virtual-byte), so picking the right fee is the difference between a transaction that confirms in the next block and one that sits in the mempool for hours. The node derives its estimate from how recent transactions at various fee rates actually got mined. Call it with positional parameters against https://bitcoin.therpc.io/YOUR_API_KEY, passing your confirmation target in blocks.

Use cases

• Choose a fee rate for a transaction you want confirmed within a specific window — for example conf_target: 6 for roughly an hour, or conf_target: 1 to aim for the next block.
• Build fast / normal / slow fee tiers in a wallet UI by issuing several calls with different conf_target values (e.g. 1, 6, 144) and presenting each resulting rate to the user.
• Surface the returned errors array when the node lacks enough recent data to produce an estimate, instead of silently proceeding with a missing fee rate.

Parameters

Response

Example request

1curl https://bitcoin.therpc.io/YOUR_API_KEY \
2  -X POST \
3  -H "Content-Type: application/json" \
4  -d '{
5  "jsonrpc": "1.0",
6  "id": "therpc",
7  "method": "estimatesmartfee",
8  "params": [
9    6,
10    ""
11  ]
12}'

Errors & troubleshooting

Common pitfalls

• The returned feerate is in BTC per kilo-virtual-byte (BTC/kvB), not sat/vB. To convert to the sat/vB figure most wallets display, multiply by 100,000 (1e5) — for example 0.00001500 BTC/kvB equals 1.5 sat/vB.
• On insufficient data the response carries an errors array and omits feerate entirely. Do not assume feerate is always present; check for it before using the value.
• conf_target must be an integer in the range 1–1008 blocks. Values outside that range are rejected with an invalid-parameter error.

Supported networks

• Mainnet
• Testnet

See also

• getmempoolinfo
• getnetworkinfo
• getblockstats