General information, not financial advice. Test any setup with a small amount first. Status 23 October 2026.
BIP39 allows an optional passphrase. The wallet combines your seed words with the passphrase to create the keys. It is often called the "25th word", but it can be any text.
How it behaves
- Every passphrase is valid. BIP39 notes that each passphrase generates a valid wallet. A typo does not give an error; it opens a different, empty wallet.
- Same words, new wallet. Seed + "summer" and seed + "Summer" are two unrelated wallets.
- BIP39 mentions this gives plausible deniability: you can keep a small decoy balance without a passphrase.
The problem it solves
If someone finds your seed phrase, they still need the passphrase. That turns a single secret into two, which can be stored apart.
The new risk
The passphrase is not stored anywhere by the wallet. Lose it, and the coins are lost, even with the seed words intact. Heirs must know it exists.
Good practice
- Write the passphrase down and store it separately from the seed.
- Use exact spelling and capitalisation; avoid characters that are hard to type on a hardware wallet.
- After setup, test: restore the wallet with seed + passphrase and check that the first receive address matches.
For many users a passphrase is a good middle step between a single seed and multisig.