Here Murch defined the rules related to RBF, as one of the techniques for fee bumping. He also posted a link to Bitcoin Core's official documentation related to the implementation of RBF (link).

However, I am interested in what are all the rules for CPFP as another fee bumping technique? Posting just the official documentation, some documentation like Murch posted, (or some similar relevant material) would also be sufficient for me.

1 Answer 1


There are no specific relay policy rules that apply to CPFP, because unlike RBF, CPFP is not a relay policy. It's a completely normal new, additional, transaction that gets relayed. The fee-bumping effect is not achieved by a special relay mechanism, but by the miner's block building mining logic recognizing the combination of child and parent as better than the parent alone.

For this to work, the block building code needs to be sufficiently powerful to recognize this. This is the case if the miner directly or indirectly uses Bitcoin Core (version 0.13.0 or later).

Note that there are general policy rules that apply to dependant transactions (e.g. the ancestor and descendant count limits, which are by default 25 transactions). They're not specific to CPFP, but may impact its use.

  • e.g. the ancestor and descendant count limits, which are by default 25 transactions So, every transaction has the ancestor and descendant count. 1) I know that descendant count includes the transaction itself, is this also the case with the ancestor count? 2) Is the limit per count 25 (25 for descendant count and 25 for ancestor count) or in total?
    – LeaBit
    Commented Dec 8, 2023 at 23:25
  • 1
    Yes, ancestor count also includes the transaction itself. The limits are configurable, but as of Bitcoin 26.0 (and ever since these concepts were introduced), the defaults have been 25 and 25. Commented Dec 8, 2023 at 23:30

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