Key takeaways
- A seed phrase is a readable backup of the master secret from which a wallet's private keys are derived.
- Whoever holds the phrase controls the coins. Bitcoin transfers cannot normally be reversed.
- Keep it offline, written or stamped, and in more than one secure place. Avoid photos, cloud notes and email.
- Legitimate wallets and support staff never need you to type or read out the phrase. Anyone who asks is attempting a scam.
- A passphrase is a separate, optional extra. Forget it and the coins are lost even if you hold the words.
For information only. Not investment advice. This guide explains how recovery phrases work. Don't invest unless you're prepared to lose all the money you invest.
The short answer
A seed phrase is the human-readable form of the secret behind a self-custody Bitcoin wallet. Most wallets follow a standard called BIP-39, which turns random data into a list of words from a fixed list of 2,048. Typing those words into a compatible wallet rebuilds the same keys and so the same coins. That makes the phrase both your backup and your biggest single point of failure.
This guide sits in the CoinCorner learn hub. It assumes you know what a private key is; if not, start with What is Bitcoin?
What a seed phrase is
Bitcoin ownership is controlled by private keys. A modern wallet does not keep a single key; it generates a whole tree of keys from one starting value, the seed. This is called a hierarchical deterministic wallet, and the Bitcoin Project developer guide describes how one backup can cover keys created later too. The seed phrase is that starting value written as words, because words are easier to copy accurately than a long string of numbers.
Two practical points follow:
- The phrase is the wallet. The device or app is replaceable. With the phrase you can restore on new hardware; without it, a broken device can mean permanent loss.
- The phrase is a bearer secret. There is no username, no second factor and no helpline at network level. See “Not your keys, not your coins” for what holding your own keys does and does not change.
How the words are made
The BIP-39 specification sets out the process. A wallet generates random data, adds a short checksum, splits the result into groups and maps each group to a word from a list of 2,048. The common lengths are:
| Words | Random data | Checksum |
|---|---|---|
| 12 | 128 bits | 4 bits |
| 24 | 256 bits | 8 bits |
The checksum lets software spot a mistyped word. The standard then stretches the phrase into the seed with a function called PBKDF2, and the wallet derives its keys from that seed. Because the word list is public, the safety of a phrase rests on the words having been chosen at random by reputable software. Never pick the words yourself.
Not every wallet uses BIP-39. Some use their own formats, so keep a note of which wallet and format a phrase belongs to; the words alone may not restore elsewhere.
The optional passphrase
BIP-39 allows an extra passphrase, sometimes called a “25th word”, that is combined with the phrase when the seed is built. Each different passphrase produces a different wallet, and a wrong one raises no error: you simply see an empty wallet. It protects against someone finding the words, but it is a second secret you must also back up. Store it separately from the phrase, or you gain nothing.
If you are not confident managing two secrets, a plain phrase stored well is usually easier to get right than a passphrase stored badly.
How to store a seed phrase
The aim is to survive both theft and accident. The guide to backing up your Bitcoin wallet covers the full routine; the essentials for the phrase are:
- Write it on paper or metal, offline. Do it yourself, in private, straight from the wallet's setup screen. Write clearly, in order, and number the words.
- Check it. Restore the wallet with a small amount first to confirm the words are correct before you rely on them.
- Keep more than one copy in different places. One fire, flood or house move should not end the backup. Paper can degrade or burn; engraved or stamped metal is more durable, though it is a convenience, not a requirement.
- Limit who knows. Tell trusted people only that a backup exists and how they could find it if you cannot, in a way that does not reveal the words.
- Plan for inheritance. Without instructions, your family may not know that the coins exist or how to reach them.
Splitting one phrase into pieces can look clever but may make recovery harder: lose one piece and the whole backup can fail. Multi-signature, where several separate keys must approve a spend, is a sturdier way to remove a single point of failure; see What is a multi-signature wallet?
Common mistakes
- Digital copies. Photos, screenshots, emails, cloud notes and chat messages can be synced, scraped or breached.
- Typing it into a website or app prompt. Fake wallet pages and “support” agents ask for the phrase to “verify” or “fix” a wallet. The FCA's guidance on crypto scams treats unsolicited help with your crypto as a warning sign.
- Using a pre-filled wallet. A device that arrives with a phrase already written down is not yours alone. Always generate your own.
- Never testing the restore. A backup that has never been used may contain a mistake you discover too late.
- Mixing up the phrase and the passphrase. Back up both, separately, and record which wallet they belong to.
Seed phrases and custodial services
If an exchange or service holds your Bitcoin, you normally have a login rather than a seed phrase, and the provider holds the keys. That trades responsibility for trust in the provider. CoinCorner's Vault is a custodial arrangement that uses multi-signature, described in How a multi-sig Vault protects your keys. Neither route is risk-free: self-custody puts loss and theft on you, and custody adds counterparty risk.
CoinCorner Ltd is registered with the Isle of Man Financial Services Authority as a designated business for anti-money-laundering oversight only. That is not a licence, and CoinCorner is not regulated by the FCA. Cryptoasset holdings are not covered by the Financial Ombudsman Service or the Financial Services Compensation Scheme. Account questions are answered in the FAQ.
Frequently asked questions
Is a seed phrase the same as a private key?
No, but they are linked. The seed phrase is a human-readable form of a master secret. Wallet software derives many private keys from it, so the phrase can restore all of them. Whoever holds the phrase can spend the coins, so treat it as the key to the whole wallet.
Can I store my seed phrase in a photo, cloud note or password manager?
It is best not to. Anything connected to the internet can be copied if the account or device is compromised, and a thief who finds the words can move the coins with no way to reverse it. Keep the phrase offline.
What happens if I lose my seed phrase?
If the wallet still works you can create a new wallet and move the coins, then back up the new phrase. If the device fails and there is no copy of the phrase, the coins are generally unrecoverable, because no company or network can reset it.
Is a 24-word phrase safer than a 12-word one?
Both are generated from random data. A 24-word phrase encodes more randomness, but the common failures are lost, stolen or photographed phrases rather than guessed ones, so how you store it matters more than its length.
What is a passphrase, and is it the same as a seed phrase?
No. A BIP-39 passphrase is an optional extra word or sentence mixed in when the seed is built. A different passphrase gives a completely different wallet. It adds protection, but if you forget it the coins are lost even when you still hold the words.
Do I need a seed phrase if I use CoinCorner's Vault?
Not for the Vault itself. Its keys are held under multi-signature arrangements managed by CoinCorner, which is a custodial service. If you also use a self-custody wallet elsewhere, that wallet has its own seed phrase to protect.
Sources
This guide was written on 26 October 2026 from the published documents below. The pages were not re-opened while drafting, so check each original for its current wording, particularly the BIP-39 text, before relying on a detail.
- Bitcoin Improvement Proposal 39, Mnemonic code for generating deterministic keys: https://github.com/bitcoin/bips/blob/master/bip-0039.mediawiki
- Bitcoin Project, Developer Guide, Wallets: https://developer.bitcoin.org/devguide/wallets.html
- Financial Conduct Authority, Crypto investment scams: https://www.fca.org.uk/consumers/crypto-investment-scams
- Financial Conduct Authority, Crypto: The basics: https://www.fca.org.uk/investsmart/crypto-basics