What a confirmation counts
When a Bitcoin transaction first appears in a block, it is commonly described as having one confirmation. Each later block adds another. A confirmation indicates inclusion in the current chain, not an absolute promise that reversal is impossible. A competing chain with more accumulated work can cause a short reorganization.
How blocks link together
The Bitcoin developer guide explains that each block links to its predecessor through a hash. Changing an earlier block therefore requires catching up with the work that followed it. This makes reversal harder as confirmations accumulate, although network hash rate and an attacker's resources also affect the risk.
A hypothetical deposit
Suppose exchange A requires one deposit confirmation while exchange B requires three. A balance may appear earlier on one platform, while withdrawal eligibility follows a different threshold. Read the service's rules for pending deposits, available balances, and how it counts confirmations.
Confirmations and reversal cost
A small transfer between personal wallets and a large exchange deposit can have different operational risk tolerances. The appropriate threshold depends on transaction size, recipient policy, and network conditions; there is no universal number that guarantees safety.
Compare exchange thresholds
Use a block explorer to check the transaction ID, included block height, and number of successor blocks. A platform's internal ledger processing can lag behind on-chain confirmations, so investigate network status and the service's deposit policy separately when crediting is delayed.
Limits of finality
Confirmation count is a probabilistic measure of increasing finality, not the same as legal settlement or permission to withdraw from a recipient service. Check the recipient's official threshold and consider both reorganization risk and platform operations.