<p>Zero- and low-fee transactions aren't <em>relayed</em> by default.  If you attempt to broadcast one over the Bitcoin peer-to-peer network, most nodes won't pass it along for you (and they might even "ban" you by refusing to relay any of your transactions for a while).  However, such transactions are still <em>valid</em>, and it is perfectly legal for a miner to confirm such a transaction by including it in a block, should they choose to do so.  So this raises two questions:</p>

<p><strong>How would they get ahold of a zero-fee transaction, if they're not relayed?</strong></p>

<ul>
<li><p>The miner might have created the transaction for themselves.  For instance, if a mining pool needs to pay its members their earnings, the pool operator could create a transaction and include it in the blocks the pool is attempting to mine.  There's no point in including a fee, because the pool would just be paying the fee back to itself.</p></li>
<li><p>Some large miners may have alternate ways to receive transactions (e.g. a web site where anyone can paste a transaction and the miner will consider it).  This is also useful for people who want to create transactions which can't be relayed because they are not <a href="https://bitcoin.stackexchange.com/questions/52528/how-is-a-standard-bitcoin-transaction-defined">standard</a>.</p></li>
</ul>

<p><strong>Why would they confirm it?</strong></p>

<p>Obviously most miners are motivated by profit and so they would prefer to confirm transactions with higher fees.  But other than altruism or bugs, here are some reasons why they might choose to confirm a zero-fee transaction.</p>

<ul>
<li><p>It's their own transaction, so there is no point in including a fee.  See above.</p></li>
<li><p>They've been paid in some other way.  Some miners have "transaction accelerators" where you can pay that specific miner some amount to "buy" faster confirmation.</p></li>
<li><p>"Child pays for parent."  If the zero-fee transaction is used as input by another "child" transaction which has a high fee, the two transactions together might have a higher average fee than any other two available transactions.  The miner can't confirm the child without also confirming the parent, but it might be worth it to collect the child's fee.</p></li>
</ul>

CC BY-SA 3.0
2018-01-20T13:51:50.163Z
(extreme edge-case) the transaction could have finished filling a block - https://en.bitcoin.it/wiki/Transaction_fees - perhaps, at that instant, there just weren't any other paying ones that fit.
Apps-n-Add-Ons
CC BY-SA 3.0
2018-01-20T01:41:14.773Z
2018-01-20T01:41:14.773Z
Nate Eldredge
<p>I thought someone said in this forum that the Bitcoin network screens out zero transaction fee-transactions because they are "dust" transactions and if anyone could submit zero-transaction-fee transactions, people could start a DOS attack and clog the system.  Then I stumbled upon this web site that lists the fees for submitted transactions</p>

<p><a href="https://bitcoinfees.earn.com/" rel="nofollow noreferrer">https://bitcoinfees.earn.com/</a></p>

<p>And there are actually a handful of zero transaction fees (as well as a few 1-10 Satoshi transaction fees).  How is this possible?  Did someone game the system and get their transactions in there?</p>

CC BY-SA 4.0
2020-05-10T16:57:12.517Z
Just for the fun of it, here is a zero fee transaction: https://www.blockchain.com/btc/tx/7957a35fe64f80d234d76d83a2a8f1a0d8149a41d81de548f0a65a8a999f6f18
Codier
<transactions><unconfirmed-transactions><transaction-fees><mempool>
How did these zero-transaction fee transactions make it into the Bitcoin network?
Dave
# How did these zero-transaction fee transactions make it into the Bitcoin network?

(Asked by: username_0 on 2018-01-20)

I thought someone said in this forum that the Bitcoin network screens out zero transaction fee-transactions because they are "dust" transactions and if anyone could submit zero-transaction-fee transactions, people could start a DOS attack and clog the system. Then I stumbled upon this web site that lists the fees for submitted transactions

<https://bitcoinfees.earn.com/>

And there are actually a handful of zero transaction fees (as well as a few 1-10 Satoshi transaction fees). How is this possible? Did someone game the system and get their transactions in there?

**Tags:** transactions, unconfirmed-transactions, transaction-fees, mempool

> **Comments:**
> **username_1**: Just for the fun of it, here is a zero fee transaction: https://www.blockchain.com/btc/tx/7957a35fe64f80d234d76d83a2a8f1a0d8149a41d81de548f0a65a8a999f6f18  

---

## 1 answers

### Answer by username_2 on 2018-01-20. Score: 7 | Accepted answer

Zero- and low-fee transactions aren't *relayed* by default. If you attempt to broadcast one over the Bitcoin peer-to-peer network, most nodes won't pass it along for you (and they might even "ban" you by refusing to relay any of your transactions for a while). However, such transactions are still *valid*, and it is perfectly legal for a miner to confirm such a transaction by including it in a block, should they choose to do so. So this raises two questions:

**How would they get ahold of a zero-fee transaction, if they're not relayed?**

* The miner might have created the transaction for themselves. For instance, if a mining pool needs to pay its members their earnings, the pool operator could create a transaction and include it in the blocks the pool is attempting to mine. There's no point in including a fee, because the pool would just be paying the fee back to itself.
* Some large miners may have alternate ways to receive transactions (e.g. a web site where anyone can paste a transaction and the miner will consider it). This is also useful for people who want to create transactions which can't be relayed because they are not [standard](https://bitcoin.stackexchange.com/questions/52528/how-is-a-standard-bitcoin-transaction-defined).

**Why would they confirm it?**

Obviously most miners are motivated by profit and so they would prefer to confirm transactions with higher fees. But other than altruism or bugs, here are some reasons why they might choose to confirm a zero-fee transaction.

* It's their own transaction, so there is no point in including a fee. See above.
* They've been paid in some other way. Some miners have "transaction accelerators" where you can pay that specific miner some amount to "buy" faster confirmation.
* "Child pays for parent." If the zero-fee transaction is used as input by another "child" transaction which has a high fee, the two transactions together might have a higher average fee than any other two available transactions. The miner can't confirm the child without also confirming the parent, but it might be worth it to collect the child's fee.

> **Comments:**
> **username_3**: (extreme edge-case) the transaction could have finished filling a block - https://en.bitcoin.it/wiki/Transaction_fees - perhaps, at that instant, there just weren't any other paying ones that fit.  

---

