What is SegWit? The Bitcoin upgrade that made room for more
By SendPay Business · · 2 min read
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SegWit, short for Segregated Witness, is an upgrade to Bitcoin that was activated in August 2017. It changed how transaction data is stored so that more transactions fit into each block.
What it changed
- Signature data, the 'witness', was moved into a separate part of the transaction.
- Blocks were measured in a new way, so more transactions could fit.
- It fixed a long-standing issue called transaction malleability, where a transaction's ID could be altered before confirmation.
Why it matters to users
SegWit transactions usually take up less counted space, so they often cost less in fees. Fixing malleability also made it safer to build payment channels on top of Bitcoin, which helped make the Lightning Network possible.
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Spotting SegWit addresses
Native SegWit addresses start with bc1. Older legacy addresses start with 1, and some wrapped SegWit addresses start with 3. Most modern wallets use bc1 addresses by default and can send to any of these types.
Where SendPay fits
SendPay platforms let customers buy, sell and hold crypto, held with regulated partners, alongside GBP, EUR and USD accounts, powered by licensed partners. SendPay doesn't offer trading tools, DeFi or lending.
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Questions people ask
What will my Bitcoin transaction cost?
Estimate its size and fee at any fee rate.
Bitcoin fee calculator →What is the Lightning Network?
A layer on top of Bitcoin for fast, cheap payments.
Lightning Network →What is the Bitcoin mempool?
The waiting area for transactions before they are added to a block.
Mempool →Read next
Spotted a mistake or something out of date? and we'll fix it. How our guides are made
This guide is general information, not legal or financial advice. SendPay Business is a technology company, not a bank, and does not take deposits; regulated services on the platforms are provided by licensed partners. Other companies named in this guide are reference points only and are not affiliated with SendPay Business.