User-entered transaction scenario · Reviewed 2026-11-03

Bitcoin RBF fee bump calculator

Estimate a Bitcoin replacement transaction's minimum modeled fee and extra sats using the original fee, replacement size, target fee rate, and relay increment.

Estimate a replacement transaction fee from transaction sizes and fee assumptions you enter. This is a lower-bound scenario, not a wallet quote or confirmation guarantee.

Original transaction fee (sat) Original transaction virtual size (vB) Replacement transaction virtual size (vB) Target replacement fee rate (sat/vB) Relay fee increment assumption (sat/vB)

Enter all five assumptions and calculate.

How this estimate works

The modeled replacement fee is the larger of (a) the target fee rate multiplied by replacement size, rounded up to a whole satoshi, and (b) the original fee plus the entered relay increment multiplied by replacement size, also rounded up. The calculator reports the implied original fee rate and the extra fee relative to the original.

Bitcoin replacement policy is more involved than this estimate. A replacement generally conflicts by spending one or more of the same inputs, and nodes may require a higher total fee to cover transactions evicted with it, an adequate feerate, and additional policy conditions. This form has no inputs for descendant fees, node mempool contents, wallet rules, or current fee conditions. Use your wallet's own fee-bump estimate and review it before signing.

RBF applies only while the original transaction is unconfirmed. Whether a replacement propagates depends on the nodes and wallet involved; a higher fee does not promise acceptance or a confirmation time.

Sources

Blockstream Help: What is Replace-by-Fee (RBF)? — explains conflicting inputs, fee increases, and wallet-dependent fee bumping.
Bitcoin Core: Mempool replacement policy — documents implementation policy requirements; node policy can vary.

Sources reviewed 2026-11-03. This browser-only calculator does not inspect a transaction, contact a node, sign or broadcast anything, or guarantee acceptance or confirmation.

How it works

Enter the original transaction fee and virtual size, replacement virtual size, your target sat/vB rate, and the node relay increment to estimate a modeled replacement fee floor.

Good to know

Does this guarantee the replacement will be accepted or confirmed?

No. This is a simplified fee estimate. Node mempool policies, the original transaction's descendants, replacement rules, wallet behavior, and changing fee conditions can require a higher fee or prevent replacement. Confirmation time is not guaranteed.

What does the relay increment input mean?

It is the additional fee-rate assumption, in sat/vB, applied to the replacement transaction's virtual size on top of the original transaction fee. Check the relevant node or wallet policy; the tool does not discover it.

Coinbase referrals — TODO: apply/approval and configure referral URL — referral link not configured.

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