One-Sentence Definition
A block confirmation happens each time a new block is added to the blockchain after the block containing your transaction, with more confirmations making the transaction increasingly secure and irreversible.
Why It Matters for Solo Mining
When you solo mine a block, exchanges and wallets typically require a certain number of confirmations before crediting your block reward to your account. Most Bitcoin exchanges require 100+ confirmations (about 16-17 hours) before you can spend your newly mined coins, which protects them from potential orphan blocks. This waiting period is something every solo miner experiences after finding a block—it’s not instant money, even though you found the block.
How It Works
When your transaction first gets included in a block, it has zero confirmations. Once that block is added to the blockchain, it receives its first confirmation. Each subsequent block built on top adds another confirmation—so 6 confirmations means 5 additional blocks were mined after the block containing your transaction.
The reason confirmations matter is because of blockchain security. A transaction with 1 confirmation could theoretically be reversed if someone created a competing chain through a fork, but reversing a transaction with 6+ confirmations would require enormous computational power. Each confirmation exponentially increases the cost and difficulty of attacking that transaction.
Different cryptocurrencies require different confirmation counts based on their block times and security models. Bitcoin typically uses 6 confirmations for significant transactions (about 1 hour), while faster blockchains might need more confirmations to achieve equivalent security. The transactions sit in the mempool before getting their first confirmation.
Example
Imagine you solo mine a Bitcoin block at height 800,000. Your block reward starts with 0 confirmations. When block 800,001 is mined by someone else, you now have 1 confirmation. At block 800,006, you have 6 confirmations and most services consider it secure. At block 800,100, you finally have the 100 confirmations most exchanges require to let you trade or withdraw your coins.
Think of it like concrete hardening—each confirmation is like waiting another hour for the concrete to set. After enough time, it’s practically impossible to change.