BIP39 Passphrase (the "25th Word") Explained: Should You Use One?
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A BIP39 passphrase is an optional extra secret you add to your recovery phrase. It can protect you if someone finds your seed words — but it can also lock you out forever if you forget it. Here is how it works, who should use one, and how to set it up without making the classic mistakes.
How a passphrase works
Under the BIP39 standard, your wallet combines the seed words with an optional passphrase to calculate the master key. Every different passphrase — including no passphrase at all — produces a completely different wallet with different addresses. There is no "wrong passphrase" error: type it differently and you simply open another, empty wallet.
That is why people call it the "25th word", although it does not have to be a word from the list. It can be any text, and it is case-sensitive: Blue Harbor and blue harbor open two different wallets.
Benefits and risks
| Benefits | Risks |
|---|---|
| Someone who finds your seed words cannot reach the hidden wallet. | Forget the passphrase and the funds are gone — nobody can reset it. |
| Protects against a stolen device plus a leaked backup. | Typos and capitalisation differences silently open the wrong wallet. |
| Lets you keep a small decoy balance in the no-passphrase wallet under duress. | Makes inheritance harder: heirs need both secrets and instructions. |
Who should use a passphrase?
- Probably yes: you hold an amount that would seriously hurt to lose, your seed backup is stored somewhere other people could access (shared home, safe deposit box), and you are organised enough to back up a second secret.
- Probably not yet: you are new to self-custody, you hold a small amount, or you have nobody who could help your family recover funds. Master a reliable seed backup first; see our seed phrase storage guide.
Choosing a strong passphrase
The passphrase only helps if an attacker who has your seed words cannot guess it. Attackers can try millions of guesses per second offline, so:
- Use several random words (for example 5–6 words chosen with dice) or a long, unusual sentence.
- Avoid names, birthdays, pet names, song lyrics and famous quotes.
- Stick to simple characters you can type reliably on the device, and decide once how you handle capitals and spaces.
Setting it up safely
- Make sure your standard seed backup is written down and tested.
- Enable passphrase entry in your wallet's settings (both Trezor Suite and Ledger devices support it; enter it on the device itself when possible, so malware cannot capture it).
- Enter your passphrase and open the hidden wallet. Write down the first receive address of this wallet.
- Close the wallet, re-open it with the passphrase and check that the same first address appears. This confirms you can type it consistently.
- Send a small test amount, then restore or re-open and confirm the balance before moving the rest.
Backing up the passphrase
Write the passphrase down — memory alone is not a backup, especially over years. Store it separately from the seed phrase, for example seed at home and passphrase at a relative's house or in a safe deposit box. Leave clear instructions for heirs that explain that both pieces exist and where to find them, without writing the secrets themselves into a will (wills can become public documents).
Remember that a passphrase protects you against someone finding your words, not against signing a malicious request: read our guide to wallet drainer scams.
Ready to move funds into your new hidden wallet? Use the same checks as in our exchange-to-hardware-wallet guide: verify the address on the device and send a test first.
Frequently asked questions
- Is a passphrase the same as my PIN?
- No. The PIN only unlocks the physical device and is reset if the device is wiped. The passphrase is part of the wallet's cryptographic secret: together with the seed phrase it determines which wallet you open, on any device.
- What happens if I mistype the passphrase?
- You will open a different, empty wallet with no error message. That is by design. If your balance looks empty, carefully re-enter the passphrase exactly, including capitals and spaces.
- Can I add a passphrase to my existing wallet?
- Adding a passphrase creates a new hidden wallet; it does not encrypt the existing one. You enable passphrase entry on the device, open the new hidden wallet, and then send your funds from the standard wallet to an address in the hidden wallet.
- How long should a passphrase be?
- Long enough that it can't be guessed if someone has your seed phrase: several random words or a long, unique sentence is better than a short clever word. Avoid names, dates and famous quotes.
- Should I store the passphrase with my seed phrase?
- No. Storing them together removes the protection. Keep them in separate locations, and make sure a trusted person or your inheritance plan explains how to find both.