Missing a word from your seed phrase

You have eleven words where there should be twelve, or twenty-three where there should be twenty-four. Perhaps one was never written down, or the paper is torn, or a word has faded to nothing. This is one of the most recoverable things that can go wrong with a backup, and it is worth knowing exactly how recoverable before paying anyone anything.

Count first. Standard phrases are 12, 15, 18, 21 or 24 words. If you have 11, you are missing one from a 12-word phrase; 23, one from 24. If you have 22, you are probably missing two from 24. The count also tells you whether you might instead have a word that is not missing but unreadable, which is an easier problem — a word you can't read covers that one.

If you know where the gap is, there are 2,048 candidates. Every word comes from the same fixed list, so a single known gap can only be filled 2,048 ways. The checksum then rules most of those out: for a 12-word phrase roughly one candidate in sixteen survives, around 128; for 24 words roughly one in 256, around eight.

If the missing word is the last one, the list is exact. The last word carries the checksum, so given the first eleven words there are exactly 128 valid last words for a 12-word phrase, and exactly 8 for a 24-word phrase. The offline checker lists them for you, on your own computer with the internet disconnected. Why the last word is special explains the arithmetic.

If you do not know where the gap is, multiply by the positions. Eleven written words leave twelve places the missing one could go, so about 24,500 candidates, of which roughly 1,500 pass the checksum. That is still small — seconds of computing — once there is something to check them against.

The thing to check against is an address. Several candidates will be valid phrases, and only one is yours. Find an address that held your funds — an old transaction, a withdrawal record from an exchange, a screenshot of the receive screen — and the search has a definite answer: the candidate whose derived address matches. Without an address, you are left restoring each valid candidate in a wallet and looking for a balance, which works for eight candidates and not for fifteen hundred.

Two missing words is harder, not hopeless. Two known gaps give about 4.2 million combinations before the checksum, and unknown positions multiply that further. With an address to check against it is a search of hours rather than seconds, on an ordinary computer. Three or more missing words from a 12-word phrase starts to become impractical, and from a 24-word phrase much sooner — anyone promising otherwise should be able to explain their arithmetic.

Keep it offline, and keep it yours. Every step here can be done without the phrase ever touching the internet, and none of it requires anyone else to see your words. A service that asks for the eleven words you have is asking for eleven-twelfths of your wallet. Our offline recovery toolkit runs the search on your machine with the network off; the lost-access worksheet helps you gather what you have before you start.