What Happens to Orphaned Blocks on the Blockchain?

Sometimes, miners will create two or more blocks from the same parent, but only one child block can remain. So, what happens to the unintegrated child blocks? 

Orphan blocks on the blockchain go back to the memory pool for validation and use in a new chain. After determining the proof of work, the network discards the losing child blocks. There are no rewards for mining orphaned blocks, but some blockchains such as Ethereum may allow for rewards. 

The rest of this article will explore the topic of orphaned blocks, including where they go, where they come from, the likelihood of them occurring, and whether they are the same thing as stale blocks. 

Where Orphaned Blocks Go on the Blockchain

Orphaned blocks go to the memory pool on a blockchain. Any verified blocks found within the shorter chain become orphan blocks – discarded blocks – and return to the memory pool for validation and addition to a new chain. 

Decentralization means that there is no central storage location for blockchain. Instead, it is in computers or systems all over the network, referred to as nodes. Each node has a copy of the blockchain or the transactions on the network. 

If a node recognizes a higher total chain than the one it presently believes to be the highest, the protocol is to bring the orphaned blocks back from the mempool. As a result, transactions will have another chance to confirm, this time on the correct chain. 

Due to the span of these unused branches being so short, people who wait for 5–6 confirmations are unlikely to notice something was wrong. 

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Where Orphaned Blocks Come From

To be valid, a block must hash to a lesser value than the current target. Every block signifies a significant amount of work done to generate it. Each block has the hash of the previous block, resulting in a chain of blocks containing a great deal of work. As a result, proof of work is necessary to validate a block. 

A blockchain contains a series of related blocks that all receive information from blocks preceding them. Miners strive to generate additional blocks during the standard mining process by solving the hash—the 8-bit number that contains the block’s info. 

The block reward goes to the first miner to open a new block successfully and publish the first transaction on it. The opened block holds information from previous blocks and recent transactions and becomes a parent for blocks that follow. 

Often, there’ll be two child blocks from one parent block, but since only one of the child blocks will join the chain, the other gets discarded. The network nodes decide which blocks to accept through a validation consensus. 

Every block will also need a link to subsequent blocks, resulting in a passive race to verify the most blocks. As determined by proof of work (PoW), the fork with the most verified blocks earns a place in the blockchain. 

An orphan block also comes about when a hacker attempts to roll back some network transactions. Keep in mind that such an action requires over 50% of the hash power in the network. 

What Is Proof of Work in Blockchain?

Proof of work (PoW) in blockchain is a consensus framework requiring network members to spend time solving a random computational problem. The main objective of the consensus framework is to prevent or discourage anyone from exploiting the system. 

The widest application of Proof of work is in cryptocurrency mining to validate transactions and generate new tokens. So why is PoW the preferred method of verification? 

Proof of work validation is too resource-intensive, which discourages anyone seeking to game the system. Other less resource-intensive proof mechanisms are available, such as proof of burn and proof of stake, but they have glaring flaws. 

For example, PoS assigns the node to mine or verify block transactions at irregular intervals based on the number of coins a node possesses. The more tokens a wallet holds, the more mining leverage it gains. While PoS requires far fewer resources, it has several failings, including a greater likelihood of a 51 percent attack and motivation to stockpile tokens rather than use them. 

Without a reliable proof mechanism, the network and the data stored within it would be vulnerable to theft or attacks. 

What Fraction of Bitcoin Blocks Becomes Orphaned?

Up to one-third of Bitcoin blocks becomes orphaned. Orphan blocks often occur and almost always by chance, so there will likely be several instances of this every week. 

This isn’t usually a cause for concern, since mining is a constant, so parent blocks will inevitably result in a certain number of orphan blocks.

Are Orphan Blocks the Same Thing as Stale Blocks?

Orphan blocks are not the same thing as stale blocks. While most people consider the terms orphan blocks and stale blocks as interchangeable, it may often not be so from a technical standpoint. 

Since the basis for block reference is ancestral relationships, it follows then that an orphan block is one with unspecified parent blocks. It also implies that the block hash was insufficient. 

A block hash is an encoded number that represents a snapshot of the entire blockchain at block creation. Typically, the hash would incorporate parent block details, and so an orphan block would be unusual in a system dependent on verification and validation. When most people talk about a rejected block, they refer to a stale block. 

A stale block can also mean any other block after an orphan block. A block can be “solved,” or the network can find a valid POW at any time. If that happens, every miner working on a particular block worldwide must pause and restart their work. After that point, working on a similar block is the same as working on outdated data and outdated transactions. 

Are Orphan Blocks a Cause for Concern?

Orphan blocks are not usually a cause for concern. If placed without malicious intent, the transactions eventually transfer into the main chain. However, be cautious if you receive an orphan block.

Caution is vital if you receive such a Bitcoin. Failing to confirm that the Bitcoin is on the main chain may cause you to find that it’s invalid when you try to spend it. This is why Bitcoin confirmations happen after six authentications to guarantee transactions are on the main chain. 


Orphaned blocks go to the mempool, so the blockchain can reuse them when it grows more extended than the ones the network thinks are the longest. If that doesn’t happen, then the particular child block gets discarded, to the disappointment of the miner. 

Every block goes through a resource-intensive proof mechanism to ensure the safety of the network. The block with the most validations joins the network, and the whole process keeps everyone safe.