Fee Estimation
Predicting the required sat/vByte rate to confirm within a certain timeframe, given current network conditions.
Fee estimation is the wallet's job of predicting how many satoshis per virtual byte (sat/vB) you need to pay to get your transaction confirmed within some target number of blocks. Pay too little and you wait; pay too much and you overpay.
The estimate is built from two signals:
- Current mempool state. How much unconfirmed transaction data is queued up at each fee rate? The fuller the mempool, the higher the floor.
- Recent block history. What fee rates were actually included in the last several blocks? This anchors the estimate to what miners are accepting right now.
Bitcoin Core exposes its own estimator via the estimatesmartfee RPC; this is what most nodes and wallets reference, sometimes blended with third-party feeds. Estimates come in tiers: next-block, ~3 blocks, ~6 blocks, ~24 blocks. Lower urgency means lower fee.
In low-traffic periods, the estimator often returns 1 sat/vB across all tiers - the relay minimum. In congestion events (Ordinals mints, exchange withdrawal storms, market panic), the next-block estimate can spike to hundreds of sat/vB in minutes.
Estimates are guesses. If you underpay and get stuck, see Fee Bumping. The live fee market is visible in the Mining rabbit hole §6 and on the Node page.
Key takeaways
- Helps users avoid overpaying or underpaying transaction fees
- Involves reading mempool backlog and recent block inclusion rates
- Can fluctuate quickly in times of sudden network activity