Blocks are added to a blockchain when a block producer (a miner in Proof of Work or a validator in Proof of Stake) gathers valid transactions, packages them with the previous block's hash and wins the network's right to publish. Every other node re-checks the block before adding it to its copy of the chain.
What problem does adding blocks solve?
Digital money can be copied, so a network needs a way to stop the same coins being spent twice. The Bitcoin whitepaper's answer was to announce every transaction publicly and have participants agree on a single history of the order in which transactions were received. Blocks are the units of that history: once a transaction is in an accepted block, any conflicting transaction that tries to spend the same coins is rejected. For the bigger picture of a transaction's journey, see how blockchain works step by step.
What are the steps to add a new block?
- Collect: Pending transactions that pass basic checks wait in each node's mempool.
- Select: The block producer chooses which transactions to include, usually prioritising higher fees, up to the block's size or gas limit.
- Assemble: It builds a candidate block: a header containing the previous block's hash, a Merkle root of the transactions and a timestamp, plus the transactions themselves.
- Win the right to publish: In Proof of Work, by finding a valid hash first; in Proof of Stake, by being the validator selected for that time slot.
- Broadcast: The new block is sent across the peer-to-peer network.
- Verify: Every node independently re-checks the block and each transaction. An invalid block is rejected, no matter who produced it.
- Extend and confirm: Nodes add the block to their chain, and every later block built on top counts as a confirmation.
How does mining add a block in Proof of Work?
Bitcoin miners repeatedly change the header's nonce and hash it, looking for a result below the current target. The network retargets difficulty every 2,016 blocks, roughly every two weeks, to keep the average block interval near 10 minutes. The winning miner's block includes a special coinbase transaction that pays the block subsidy plus all fees in the block. The subsidy has been 3.125 BTC since the April 2024 halving; Bitcoin halving explained covers the schedule. Coinbase rewards cannot be spent for 100 blocks, which protects against rewards from blocks that later drop out of the chain.
How do validators add a block in Proof of Stake?
On Ethereum, time is split into 12-second slots. In each slot one validator is pseudo-randomly chosen to propose a block, using an algorithm called RANDAO and weighted by effective balance. Other validators attest to the block they see as the head of the chain. Once validators holding two-thirds of staked ETH have voted for it, the block is finalised, about 15 minutes after it was proposed. The more validators attest to a block, the larger the proposer's reward; validators who sign conflicting blocks are slashed. Our guide to proof of work vs proof of stake compares the two designs in full.
BNB Smart Chain uses Proof of Staked Authority: elected validators, from an active set of 45, take turns producing blocks with a 0.45-second target, and blocks usually finalise within two blocks. The guide to what BNB Smart Chain is explains how that validator set is chosen.
How do Bitcoin, Ethereum and BNB Smart Chain compare?
| Network | Who adds blocks | How they are chosen | Reward | Target interval | Finality |
|---|---|---|---|---|---|
| Bitcoin | Miners | First to find a valid Proof of Work | Block subsidy (3.125 BTC) plus fees | About 10 minutes | Probabilistic; six confirmations is a common benchmark |
| Ethereum | Validators | Pseudo-random selection (RANDAO), weighted by effective balance | New ETH issuance plus priority fees; the base fee is burned | 12-second slots | About 15 minutes |
| BNB Smart Chain | Validators (PoSA) | Rotation among elected validators ranked by staked BNB | Mainly transaction fees | 0.45 seconds | Within two blocks in most cases |
What happens when two blocks are found at the same time?
Occasionally two valid blocks appear at the same height, creating a temporary fork. Nodes keep building on the block they saw first until one branch pulls ahead; in Proof of Work, nodes follow the valid chain with the most accumulated work. The losing block becomes stale, and its transactions return to the mempool to be included later.
This is why recipients wait for confirmations. Bitcoin.org notes that six confirmations are often considered as safe as waiting six months on a credit card transaction. Proof of Stake and BFT-style systems remove this uncertainty once a block is finalised; our overview of blockchain consensus mechanisms explains how each design reaches finality.
Confirmations at Wealtii: USDT deposits on BNB Smart Chain (BEP-20) are credited to your Wealtii account after 12 block confirmations. At BNB Smart Chain's 0.45-second target block time, 12 blocks represent only a few seconds of block production. See how Wealtii works for the full deposit process.
Frequently Asked Questions
How are new blocks added to a blockchain?
A miner or validator collects pending transactions, builds a block that references the previous block's hash, and earns the right to publish it under the network's consensus rules. Every other node re-checks the block before adding it to its own copy of the chain.
What is crypto mining?
Mining is the Proof of Work process of repeatedly hashing a block header until the result falls below a target. The first miner to succeed adds the block and earns the block subsidy plus the transaction fees.
How long does it take to add a block?
It depends on the network. Bitcoin targets about 10 minutes per block, Ethereum uses 12-second slots, and BNB Smart Chain targets 0.45 seconds.
What is a block confirmation?
A confirmation counts how many blocks have been added on top of the block that contains your transaction. More confirmations make a reversal less likely; six is a common benchmark for Bitcoin.
Sources & References
- Nakamoto, S. (2008) — Bitcoin: A Peer-to-Peer Electronic Cash System (accessed 21 Oct 2026)
- Bitcoin Developer Guide — Block Chain (difficulty, coinbase maturity) (accessed 21 Oct 2026)
- ethereum.org — Block proposal (accessed 21 Oct 2026)
- ethereum.org — Proof-of-stake (accessed 21 Oct 2026)
- BNB Chain Docs — BNB Smart Chain introduction (accessed 21 Oct 2026)
Disclaimer: This content is for educational purposes only and does not constitute financial, tax, or legal advice. Digital assets are volatile and carry risk of loss. Wealtii is early-stage and is not regulated by any financial authority.
