# Transaction IDs (txid)

A txid is the double SHA-256 hash of a transaction, shown in reverse byte order. Learn how it is made, where to find it and how to look one up.

Canonical page: https://mybitcoinexplorer.com/learn/transaction-id-txid
Topic: Transactions
Published: 2026-10-29
Updated: 2026-10-30


## A fingerprint of the transaction
A transaction ID is created by [hashing](https://mybitcoinexplorer.com/learn/hash-functions) the transaction's data twice with [SHA-256](https://mybitcoinexplorer.com/learn/sha-256). Change one byte and the txid changes completely.

> Diagram: How a txid is made — Transaction data: without witness → SHA-256 → SHA-256 → *Reverse bytes: display order → txid: 64 hex characters

## Why reversed?
Internally Bitcoin treats the hash as a little-endian number. Explorers and wallets show it reversed so it reads like a normal big-endian number. See [Bytes and endianness](https://mybitcoinexplorer.com/learn/bytes-and-endianness). If you hash a raw transaction yourself, remember to reverse the result.

## txid vs wtxid
- **txid** hashes the transaction **without** [Witness data](https://mybitcoinexplorer.com/learn/witness-data). Because signatures are left out, a third party can't change the txid by tweaking a signature (a problem called malleability, fixed by [Segregated Witness (SegWit)](https://mybitcoinexplorer.com/learn/segwit)).
- **wtxid** includes the witness. It is used inside blocks to commit to witness data.

### Worked example: A famous txid
The genesis block's only transaction has txid `4a5e1e4baab89f3a32518a88c31bc87f618f76673e2cc77ab2127b7afdeda33b`. It is also the [Merkle trees and the merkle root](https://mybitcoinexplorer.com/learn/merkle-root) of [block 0](/block/0), because a block with one transaction has that transaction's hash as its root.



## Where to find your txid
- **In your wallet:** open the payment's details; look for "transaction ID", "txid" or "hash".
- **From an exchange:** withdrawal history usually links the txid.
- **On MyBitcoinExplorer:** paste it into the [search](/explorer) to see status, fee and confirmations.

## Why the txid can change before confirmation
If a payment is replaced with [RBF](https://mybitcoinexplorer.com/learn/replace-by-fee-rbf) to raise its fee, the new version is a different transaction with a new txid. The old txid will never confirm. Always check the latest txid your wallet shows.


## Key takeaways

- A txid is the double SHA-256 of the transaction without witness data.
- It's displayed in reversed byte order.
- Excluding the witness makes txids immune to signature malleability.

## Common questions

### Can two transactions have the same txid?

In practice no. Finding two different transactions with the same SHA-256 hash is considered infeasible.

### Why can't I find my txid in an explorer?

It may not have reached that node yet, may have been replaced, or the explorer may need a transaction index for old transactions.

### Is a txid secret?

No. It's public and safe to share. It reveals the transaction, which is already public.

### Is the txid the same as a transaction hash?

Usually yes. Some tools also show the wtxid, which includes witness data.

## Related lessons

- [SHA-256](https://mybitcoinexplorer.com/learn/sha-256)
- [Bytes and endianness](https://mybitcoinexplorer.com/learn/bytes-and-endianness)
- [How to look up a Bitcoin transaction](https://mybitcoinexplorer.com/learn/how-to-look-up-a-transaction)
- [Witness data](https://mybitcoinexplorer.com/learn/witness-data)