Seed Phrase
Also: mnemonic, recovery phrase, backup phrase
wallets · beginner
12 or 24 English words encoding the entropy that derives every key in a wallet. Lose it, lose the coins.
A seed phrase is the human-readable backup of a Bitcoin wallet. It encodes 128 or 256 bits of [entropy](/glossary/entropy) as 12 or 24 words drawn from a fixed 2048-word list defined by [BIP-39](/glossary/bip39).
Each word represents 11 bits. A 12-word phrase carries 128 bits of entropy plus a 4-bit checksum (132 ÷ 11 = 12). A 24-word phrase carries 256 bits plus 8 bits of checksum. The checksum catches typos: a random 12-word sequence has only a ~1-in-16 chance of validating.
The words themselves are not the seed material. They feed [PBKDF2-HMAC-SHA512](/glossary/pbkdf2) — 2048 rounds, salted with "mnemonic" + passphrase — producing a 64-byte seed. That seed is the input to [BIP-32](/glossary/bip32), which deterministically derives every key in the wallet. The optional passphrase ("25th word") changes the salt, producing a different wallet for each passphrase value — used by some for plausible-deniability vaults.
Operational rules:
- The phrase IS the wallet. Anyone who can read it can spend.
- Write it down on paper or metal; never type it into a website. Phishing pages mimicking real wallets are the number-one cause of seed-phrase theft.
- Hardware wallets exist specifically so the phrase is generated by, and lives on, a device whose only job is to keep it offline.
- Do not split a 24-word phrase into "12 here, 12 there." Half a phrase leaks more than half the entropy and is not a real security improvement. Use multisig or SLIP-39 if you need true sharding.