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Lesson 10 / 21 · Advanced

Fee changes: RBF and CPFP

Understand two mechanisms before relying on a rescue button.

14 MIN WITH PRACTICEREAD → TRY → REFLECTNO WALLET NEEDED

By the end, you’ll be able to…

  • Compare replacement and child-pays-for-parent concepts.
  • Recognize wallet and policy constraints.
Your learning map

Three questions to carry into this lesson.

01Compare replacement and child-pays-for-parent concepts.
02Recognize wallet and policy constraints.
Use these goals to guide your reading. Try the paper exercise, then explain the result in your own words.

A replacement changes the proposed spend

Replace-by-fee concerns replacing an unconfirmed transaction with a competing transaction that pays a more attractive fee under applicable node policy. BIP 125 documents an opt-in approach; actual software policy can evolve. A replacement can change the transaction identifier and may change outputs, so an application must reconcile the final transaction rather than trusting an old identifier forever.

A child can make a package more attractive

Child-pays-for-parent uses a transaction spending an output of an unconfirmed parent. A sufficiently attractive combined fee can encourage inclusion of the package under supported policies. This requires a spendable output and appropriate wallet behavior. It is not a universal ability to modify somebody else’s transaction or to force a miner to include it.

Plan observability before urgency

An artist checkout should keep order identity separate from transaction identity because replacement and multiple payment attempts complicate the mapping. A fee bump is not a new sale. Before a real action, inspect the current wallet documentation, transaction state, amounts and total fee. This course provides a paper comparison only; it does not instruct you to use a paid acceleration service or modify a live transaction.

Your turn / A paper experiment

Practice on paper

A pending payment changes from identifier A to identifier B after an authorized fee replacement. What should an invoice system preserve?

I’ve tried it — show the worked answer

It should preserve the order and intended payment relationship while tracking the replacement and final settlement. It must avoid counting A and B as two independent settled donations.

Want to explore with buttons and instant feedback? Try the practice lab ↗

Think it through

Make a choice. Discover why.

Choose an answer and check the explanation. You can retry as often as you like. These are practice questions, not a test of mastery; answers are not saved or sent.

1. Does fee replacement guarantee a specific confirmation time?
  • Yes
  • No
Read the explanation

No. Mining and policy remain relevant.

2. Does CPFP let anyone spend an output they cannot authorize?
  • Yes
  • No
Read the explanation

No. The child still needs valid spending authorization.

One idea to take with you

A fee-management action needs its own reconciliation trail.

Your learning, at your pace

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