What is a seed phrase?
A seed phrase is 12 or 24 ordinary words, and for all practical purposes it is your bitcoin.
A seed phrase is a list of 12 or 24 words that your wallet generates when you set it up. Those words can rebuild every key and address in the wallet on any compatible device, so whoever has them controls the bitcoin. Write them on paper or stamp them into metal, keep them offline, and never type them into a phone, computer, or website.
What the words are
Your wallet starts by picking a huge random number, and that number is the real secret. The words are a way to write it down without mistakes, because nobody can copy a 39-digit number by hand and get it right every time.
Most Bitcoin wallets follow a standard called BIP39, which uses a fixed list of 2,048 English words. Each word stands for 11 bits of the random number, and the last word carries a small checksum, so a wallet can usually tell when you typed a word wrong. Twelve words encode 128 bits of randomness, and 24 words encode 256 bits.
BIP39 also allows 15, 18, and 21 words, but you will almost never see those outside the standard 12 and 24.
Why the seed phrase is the wallet
Your bitcoin is recorded on the Bitcoin blockchain. Your hardware wallet holds the keys that let you spend it, and every one of those keys is calculated from the seed phrase.
If your hardware wallet breaks, gets lost, or falls in a lake, you lose nothing: buy a new one, type in the words, and your bitcoin is back. If you lose the words, or someone else sees them, you can lose everything, because anyone with the words can restore the wallet on their own device, from anywhere in the world, without touching yours.
How to write it down and store it
- 1When the wallet shows the words, write them in pen on the card that came in the box, in order, with their numbers.
- 2Check every word against the screen twice. Most wallets quiz you on a few words before they finish setup, so take the quiz seriously.
- 3Copy the words onto metal if you can, because paper burns and floods. My seed storage guide ranks the steel plates and capsules worth buying.
- 4Store the backup where a burglar is unlikely to look and a house fire cannot reach. Many people also keep a second copy at a different location.
- 5Do a recovery test: wipe the device (or use a second one) and restore it from your written words with a small amount of bitcoin in the wallet. If the addresses match, your backup works.
What never to do with a seed phrase
- Never type it into a phone, laptop, password manager, cloud note, or email draft. Anything connected to the internet can leak it.
- Never photograph it, because phones often sync new photos to a cloud account automatically.
- Never enter it on a website. No real wallet company, exchange, or support agent will ever ask for it, so anyone who does is stealing from you.
- Never use an online seed phrase generator. The site that made the words can keep a copy.
- Never split the words into "half here, half there" as a security trick. A thief who finds one half has far fewer words left to guess, and if either half is lost, so is the wallet. If you want a backup that needs more than one location, use multisig instead.
Seed phrase vs private key vs passphrase
| Term | What it is |
|---|---|
| Seed phrase | The 12 or 24 words. One seed creates every key in the wallet. |
| Private key | One key for one address, calculated from the seed. A wallet can calculate as many as it needs. |
| Passphrase | Optional extra text, such as a word or a sentence, added to the seed. Every passphrase opens a different wallet, as my passphrase guide explains. |
| PIN | Unlocks the device in your hand. It does not protect the seed if someone finds your written words. |
Frequently asked questions
Is a seed phrase the same as a recovery phrase?
Yes. Seed phrase, recovery phrase, mnemonic, and backup words all mean the same thing: the BIP39 word list your wallet gives you at setup.
Can I use my seed phrase on any wallet?
Usually. Any wallet that supports BIP39 can restore it, which covers most Bitcoin wallets. If the new wallet shows a zero balance, the old one probably used a different address type or a passphrase. Check the address type setting before you panic.
Is 12 words enough, or do I need 24?
Twelve words are 128 bits of randomness, far too many possibilities for any computer to search. Twenty-four words add margin but no practical extra safety against guessing. The bigger risk is someone finding your written words, which is the same for both.
What happens if I lose my seed phrase but still have the hardware wallet?
You can still spend, so move your bitcoin to a new wallet with a new seed phrase right away, and back that one up properly. Until then, losing or breaking that device means losing the bitcoin.
Can someone guess my seed phrase?
Not if your wallet generated it properly. There are 2 to the power of 128 valid 12-word phrases. The guessable ones were never random, for example words a person made up or words from a generator website.