By What Happens When You Send Bitcoin?
Tapping "send" in a wallet app feels instant. What actually happens between that tap and the funds being irreversibly transferred involves your private key, a global network of strangers, and a queue with no fixed length. Here's the full path.
Step one: your wallet builds and signs the transaction
Your wallet assembles a transaction referencing specific previous outputs you're allowed to spend, called UTXOs (unspent transaction outputs), and specifies where the funds should go. It then uses your private key to produce a digital signature over that transaction data. This signature is what proves the transaction was authorized by whoever controls the private key, without ever revealing the key itself.
Step two: broadcast to the network
The signed transaction gets sent out to nodes across the Bitcoin network, which relay it to each other. Each node independently verifies the signature is valid and that you're not trying to spend funds you don't actually control, before passing it along. This is why a confirmed Bitcoin transaction can't simply be faked; every node checks it against the actual rules, not just trusts the sender.
Step three: waiting in the mempool
Valid but not-yet-mined transactions sit in a holding area called the mempool. Miners pick transactions from this pool to include in the next block, generally prioritizing ones that pay a higher fee per byte of data, since block space is limited and fees are optional income on top of the block reward. During busy periods the mempool can back up, meaning lower-fee transactions may wait longer.
Step four: mined into a block
Once a miner successfully finds a valid proof-of-work for a block that includes your transaction, it's added to the blockchain. At that point it has one confirmation. Each subsequent block mined on top of it adds another confirmation, and each one makes reversing it exponentially more computationally expensive, which is why receivers of high-value transactions often wait for several confirmations, commonly six, before treating funds as fully settled.
Why it's effectively irreversible
There's no institution to call to reverse a confirmed Bitcoin transaction. Undoing it would require rewriting the blockchain from that block forward faster than the rest of the honest network extends it, the same practical barrier that protects the entire transaction history. This is exactly why double-checking a destination address before sending matters so much: the network has no concept of "undo."
The private key for every Bitcoin wallet on Earth is on this website, even Satoshi's. But even if you try for a million years, you'll never find a funded one.
Try the key collider nowIn short
Sign with your private key, broadcast to the network, wait in the mempool, get mined into a block, then accumulate confirmations. For how that mining step actually works, see how Bitcoin mining works, or for what the address you're sending to actually represents, see what a Bitcoin address is.