<p>As Pieter <a href="https://bitcoin.stackexchange.com/a/102044/5406">wrote</a> in his answer, <code>modified fee</code> indicates that the node operator instructed his node to treat a transaction as if it had a higher fee. However, I think that you might be asking due to a misconception of how RBF affects transactions.</p>
<p>Most transactions are immutable: once they have been defined, the signatures on the inputs commit to the transaction's exact content and composition. Updating the fee of a transaction would require at least changing some output amounts. However, changing even one byte of the transaction would invalidate the signatures. (The exception is <a href="https://bitcoin.stackexchange.com/q/21994/5406">transaction malleability</a>, which seems irrelevant in the context, so I'm going to ignore that here.) Therefore, transactions cannot be updated.</p>
<p>However, <a href="https://github.com/bitcoin/bips/blob/master/bip-0125.mediawiki" rel="nofollow noreferrer">BIP-125 Opt-in Full Replace-by-Fee Signaling</a> specifies how to mark transactions as <em>replaceable</em> which causes nodes to allow conflicting transactions with higher fees to supersede them. While the old transaction remains unchanged and valid in that case, the newer transaction is more lucrative to miners and therefore expected to be prioritized.</p>

CC BY-SA 4.0
2021-01-30T22:40:20.390Z
This is all correct, but I don't think it has anything to do with the "modified fee" reported by Bitcoin Core mempool RPCs.
Pieter Wuille
CC BY-SA 4.0
2021-01-31T00:26:56.677Z
Hello, Thank you. That was exactly the thing I was looking for. Special thanks.
Motiv
CC BY-SA 4.0
2021-01-31T00:37:54.700Z
@PieterWuille: That's right, but it looks like you answered the question, and I answered the underlying question why they were asking in the first place. :) TBH, I didn't quite understand what they meant with "modified fee", but the "Why does nobody accelerate their transaction?" seemed like a good lead. I only understood the question fully now that I saw your answer, and their reaction to our answers, though.
Murch
CC BY-SA 4.0
2021-01-31T01:00:43.697Z
I still don't understand what that has to do with modifying transactions, but ok!
Pieter Wuille
CC BY-SA 4.0
2021-01-31T01:01:51.020Z
My read is that Motiv thought RBF would leave transactions with the same txid, but a modified fee.
Murch
CC BY-SA 4.0
2021-01-31T01:10:18.247Z
Ah, I was wondering where the RBF came from, but the given tag was a hint.
Pieter Wuille
CC BY-SA 4.0
2021-01-30T22:16:25.317Z
2021-01-31T01:05:23.247Z
2021-01-31T01:05:23.247Z
Murch
<blockquote>
<p>I can not see any transaction resting in Mempool having different values for Fee and Modified Fee fields?</p>
</blockquote>
<p>That's probably because you haven't modified any.</p>
<p>The <code>prioritisetransaction</code> RPC exists for miners to signal that particular transactions are paid for out of band, or are the miner's own transactions that should prioritized for block construction over what is implied by their feerate.</p>
<p>If you're not a miner, there is no need to ever use this RPC, and the fee and modified fee will be identical for all transactions.</p>

CC BY-SA 4.0
2021-01-31T00:29:41.337Z
Hello, I am looking at the integrated pool of transactions waiting in Mempool and I can not see any modified transaction there. I expected to see some at least in a month or in 6 months. Thank you
Motiv
CC BY-SA 4.0
2021-01-31T00:54:36.793Z
Have you ever invoked the `prioritisetransaction` RPC on your own node? If not, the modified fee will always be identical to the normal fee, because you haven't modified any. The "modified fee" is not a global network-wide property; it's local to your own node, and unless you're a miner, you never need it.
Pieter Wuille
CC BY-SA 4.0
2021-01-31T01:11:31.187Z
Reading the other comments I can maybe clarify better: the "modified fee" field in the RPC output has **nothing to do** with RBF. It's a mechanism for miners to accelerate their own transactions.
Pieter Wuille
CC BY-SA 4.0
2021-01-30T22:13:32.837Z
2021-01-30T22:13:32.837Z
Pieter Wuille
<p>I do not see any transaction in the mempool having differing values for the <code>fee</code> and <code>modified fee</code> fields. Does nobody modify or accelerate their transactions?
How do transactions with modified fees show up in the mempool?</p>

CC BY-SA 4.0
2020-08-22T01:00:47.903Z
What software are you using to inspect transactions?
Murch
CC BY-SA 4.0
2020-08-24T15:14:08.840Z
I have access to the transactions through JSON file receiver which will be called every 1 minute.
Motiv
CC BY-SA 4.0
2020-08-24T20:04:54.647Z
I meant, what is the source of the transaction data? Is it Bitcoin Core or a different Bitcoin implementation?
Murch
CC BY-SA 4.0
2020-08-25T16:28:46.677Z
official bitcoin core implementation
Motiv
CC BY-SA 4.0
2021-01-31T00:49:03.987Z
Hi Motiv, I've edited your question to make it clearer what was being asked. I was struggling with the last sentence of your original post. Did I get the meaning of that right? Please feel free to edit it further, otherwise. Thank you.
Murch
<transaction-fees><mempool><replace-by-fee>
Why are the fee value and modified fee value always the same?
Motiv
# Why are the fee value and modified fee value always the same?

(Asked by: username_0 on 2020-08-21)

I do not see any transaction in the mempool having differing values for the `fee` and `modified fee` fields. Does nobody modify or accelerate their transactions?
How do transactions with modified fees show up in the mempool?

**Tags:** transaction-fees, mempool, replace-by-fee

> **Comments:**
> **username_1**: What software are you using to inspect transactions?  
> **username_0**: I have access to the transactions through JSON file receiver which will be called every 1 minute.  
> **username_1**: I meant, what is the source of the transaction data? Is it Bitcoin Core or a different Bitcoin implementation?  
> **username_0**: official bitcoin core implementation  
> **username_1**: Hi username_0, I've edited your question to make it clearer what was being asked. I was struggling with the last sentence of your original post. Did I get the meaning of that right? Please feel free to edit it further, otherwise. Thank you.  

---

## 2 answers

### Answer by username_1 on 2021-01-30. Score: 0 | Accepted answer

As username_2 [wrote](https://bitcoin.stackexchange.com/a/102044/5406) in his answer, `modified fee` indicates that the node operator instructed his node to treat a transaction as if it had a higher fee. However, I think that you might be asking due to a misconception of how RBF affects transactions.

Most transactions are immutable: once they have been defined, the signatures on the inputs commit to the transaction's exact content and composition. Updating the fee of a transaction would require at least changing some output amounts. However, changing even one byte of the transaction would invalidate the signatures. (The exception is [transaction malleability](https://bitcoin.stackexchange.com/q/21994/5406), which seems irrelevant in the context, so I'm going to ignore that here.) Therefore, transactions cannot be updated.

However, [BIP-125 Opt-in Full Replace-by-Fee Signaling](https://github.com/bitcoin/bips/blob/master/bip-0125.mediawiki) specifies how to mark transactions as *replaceable* which causes nodes to allow conflicting transactions with higher fees to supersede them. While the old transaction remains unchanged and valid in that case, the newer transaction is more lucrative to miners and therefore expected to be prioritized.

> **Comments:**
> **username_2**: This is all correct, but I don't think it has anything to do with the "modified fee" reported by Bitcoin Core mempool RPCs.  
> **username_0**: Hello, Thank you. That was exactly the thing I was looking for. Special thanks.  
> **username_1**: @username_2: That's right, but it looks like you answered the question, and I answered the underlying question why they were asking in the first place. :) TBH, I didn't quite understand what they meant with "modified fee", but the "Why does nobody accelerate their transaction?" seemed like a good lead. I only understood the question fully now that I saw your answer, and their reaction to our answers, though.  
> **username_2**: I still don't understand what that has to do with modifying transactions, but ok!  
> **username_1**: My read is that username_0 thought RBF would leave transactions with the same txid, but a modified fee.  
> **username_2**: Ah, I was wondering where the RBF came from, but the given tag was a hint.  

---

### Answer by username_2 on 2021-01-30. Score: 2

> I can not see any transaction resting in Mempool having different values for Fee and Modified Fee fields?

That's probably because you haven't modified any.

The `prioritisetransaction` RPC exists for miners to signal that particular transactions are paid for out of band, or are the miner's own transactions that should prioritized for block construction over what is implied by their feerate.

If you're not a miner, there is no need to ever use this RPC, and the fee and modified fee will be identical for all transactions.

> **Comments:**
> **username_0**: Hello, I am looking at the integrated pool of transactions waiting in Mempool and I can not see any modified transaction there. I expected to see some at least in a month or in 6 months. Thank you  
> **username_2**: Have you ever invoked the `prioritisetransaction` RPC on your own node? If not, the modified fee will always be identical to the normal fee, because you haven't modified any. The "modified fee" is not a global network-wide property; it's local to your own node, and unless you're a miner, you never need it.  
> **username_2**: Reading the other comments I can maybe clarify better: the "modified fee" field in the RPC output has **nothing to do** with RBF. It's a mechanism for miners to accelerate their own transactions.  

---

