Bitcoin Transaction

Overview

Meaning and scope

A Bitcoin transaction is a serialized data structure that consumes existing unspent transaction outputs and creates new outputs. Inputs reference prior UTXOs and provide authorization, while outputs specify value and spending conditions. The difference between total input and output value becomes the miner fee. A transaction can be broadcast before confirmation, replaced or conflicted while pending, and reorganized after initial inclusion.

Mechanism and operation

A wallet constructs a Bitcoin transaction by selecting UTXOs that provide enough value for the intended payment and fee. It creates one or more recipient outputs and normally a change output back to the wallet. Each input references a previous transaction ID and output index. The witness or unlocking data proves that the spender satisfies the referenced output’s Bitcoin Script. Nodes verify signatures, scripts, input availability, amounts, weight, and consensus rules. Transaction size is measured through weight and virtual bytes, which affect fees. Adding more inputs usually costs more than adding simple outputs.

Practical payment example

A retailer sees a Bitcoin transaction paying its invoice. The system first verifies the destination outputs and amount, then monitors confirmation status; merely receiving a transaction ID does not establish final settlement.

Operational checks

Fee rate determines competitiveness during congestion, while absolute fee alone can be misleading. A transaction ID identifies the serialized transaction under protocol rules. Payment systems should store the transaction ID, block hash, output index, amount, and confirmation status. Replace-by-fee policies or conflicting spends can change which transaction confirms.

Distinctions and limits

A Bitcoin transaction is not identical to a payment. Reliable business processing must inspect the exact output and connect it to an invoice or account rather than using total transaction value.

Related reading

Related definitions: transaction, transaction ID.