# Segregated Witness (SegWit)

SegWit (2017) moved signatures into a separate witness section, fixing malleability, discounting signature data and making Lightning practical.

Canonical page: https://mybitcoinexplorer.com/learn/segwit
Topic: Bitcoin Script
Published: 2026-10-29
Updated: 2026-10-30


## What changed
SegWit activated at [block 481,824](/block/481824) in August 2017. It **segregates** (separates) the **witness**, meaning signatures and public keys, from the rest of the transaction.

> Diagram: Witness bytes count a quarter as much toward block weight — 82,108

## Three big effects
1. **Malleability fixed.** The [txid](https://mybitcoinexplorer.com/learn/transaction-id-txid) no longer includes signatures, so nobody can change a txid by tweaking a signature. That made the [The Lightning Network](https://mybitcoinexplorer.com/learn/lightning-network) practical.
1. **More capacity.** Blocks are measured by [weight](https://mybitcoinexplorer.com/learn/transaction-size-and-weight) and witness data is discounted, so more transactions fit.
1. **Script upgrades.** SegWit outputs carry a version number, so new script types can be added cleanly. [Taproot](https://mybitcoinexplorer.com/learn/taproot) is version 1.

## SegWit output types
| Type | Address | Holds |
|---|---|---|
| P2WPKH | bc1q… (42 chars) | 20-byte public key hash |
| P2WSH | bc1q… (62 chars) | 32-byte script hash |
| P2SH-P2WPKH | 3… | SegWit wrapped in [Pay to script hash (P2SH)](https://mybitcoinexplorer.com/learn/p2sh) for old wallets |

## A soft fork
Old nodes see SegWit outputs as "anyone can spend", but upgraded nodes enforce the real rules, and miners follow them. Old nodes stay compatible. See [Soft forks and hard forks](https://mybitcoinexplorer.com/learn/soft-forks-and-hard-forks).


## See the activation block
[Block 481,824](/block/481824) on MyBitcoinExplorer is where SegWit rules began being enforced in August 2017. Transactions after it can carry witness data; blocks can hold more than 1 MB.

## Is SegWit still used?
Yes, heavily. Native SegWit (bc1q) remains one of the most common output types, alongside Taproot (bc1p).


## Key takeaways

- SegWit separated signatures into a witness section in 2017.
- It fixed txid malleability and discounted witness data.
- It introduced versioned outputs; Taproot is version 1.

## Common questions

### Do I need SegWit?

Using a bc1q or bc1p wallet means lower fees. Every major wallet supports it.

### Is SegWit the same as SegWit2x?

No. SegWit2x was a separate, abandoned proposal to also double the block size by hard fork.

### Does SegWit lower fees?

Yes. Witness data is discounted, so SegWit inputs cost less to spend.

### Is SegWit compatible with old wallets?

Old wallets can still send to nested SegWit (3…) addresses; modern wallets support bc1 addresses directly.

## Related lessons

- [Witness data](https://mybitcoinexplorer.com/learn/witness-data)
- [Transaction size, weight and vbytes](https://mybitcoinexplorer.com/learn/transaction-size-and-weight)
- [Taproot](https://mybitcoinexplorer.com/learn/taproot)
- [Soft forks and hard forks](https://mybitcoinexplorer.com/learn/soft-forks-and-hard-forks)