Seed Phrase: How to Store It So You Don't Lose Your Bitcoin

A seed phrase is twelve or twenty-four words your wallet shows you at first start-up. For most people with crypto, it’s the most valuable sheet of paper in the house. Whoever has it can withdraw everything without knowing the PIN or holding the device. Whoever doesn’t have it, and has lost the device, has a problem with no solution.

This guide covers how to write it down, where to keep it and how to check that the backup works. The wider context of securing crypto is in the pillar how to secure crypto.

What a seed phrase is

A seed phrase, also called a recovery phrase, is one large random number written as words from a list of 2,048 entries. The rules are set by the BIP39 standard. Each word encodes 11 bits. Twelve words are 128 bits of entropy plus 4 bits of checksum, twenty-four words are 256 bits plus 8 bits of checksum. From this number all your keys and addresses are derived in a wallet that follows the BIP32 standard.

Three practical things follow.

The seed isn’t tied to a device. If a Trezor, a BitBox or other hardware breaks, you type the words into a new one and see the same funds. The words are a backup of the whole wallet, not of one device.

Word order matters. Swapping two words gives a different number, so a different wallet. The checksum catches many errors but not all. Don’t count on the device telling you something is wrong.

There’s no password reset. No company, including the wallet maker and us, can recover the funds without the words. That’s why everything below is about the backup.

How many words: 12 or 24

BIP39 allows 12, 15, 18, 21 and 24 words. In practice you’ll meet 12 and 24 most often. They differ in length: 128 bits of entropy against 256. Both give security that can’t be broken by guessing, and in practice the risk lies in how you store the backup, not in the number of words.

The device sets the number of words when it creates the wallet. If you have a choice, 24 words give a bigger margin for the future, and the cost is a longer record and a bigger chance of a slip when copying. Don’t change the variant in an existing wallet. A change means a new seed and moving the funds.

Paper or steel

Paper is the cheapest and enough to start, but it has flaws: it fades, soaks through and burns. A steel plate is the metal equivalent, with the words or their first letters stamped or assembled from pieces. In its guide, Trezor recommends stamping a 12 or 24-word backup in metal, because paper is vulnerable to fire and water. There are several makers of steel plates. You buy them yourself from the manufacturer, and we help you choose.

Medium	Fire	Water	Lifespan	Approximate cost
Sheet of paper, waterproof pen	Poor, burns	Poor, soaks through	Many years, but paper yellows and crumbles	Practically zero
Paper in a sleeve, in a safe	Depends on the safe	Better than bare paper	Similar to paper	Cost of the safe or deposit box
Steel plate (stamped or assembled letters)	Good, check the maker’s claim	Good	Very long	From a small outlay for a simple plate to several times more for sets with claimed tests
Two plates in two places	Independent fire risk in each place	As above	As above	Double the cost of a plate

Prices are only approximate, because manufacturers change them. Fire and water resistance depends on the specific model, so check the maker’s claim and test results before you believe the label “fireproof”. Steel doesn’t protect against theft. Whoever finds the plate has the funds.

How to write it down without mistakes

Most mistakes happen when copying, not when storing. A few rules help.

1. Write the words slowly, one at a time, with a number beside each. The number helps you spot a missing word.
2. Use block capitals, clearly, with a waterproof marker or a gel pen. Pencil rubs off, a cheap felt-tip fades.
3. Write the words as you see them on the device, in the original spelling. The BIP39 list is in English, so don’t translate the words or replace them with synonyms.
4. After writing, read each word from the paper and compare it with the screen. Then ask the device to verify, if it has that function, and finish with a full restore test.
5. Do the writing in a closed room, with no cameras, guests or smart speakers switched on.

Make the steel copy only after the paper one has passed a restore test. When stamping letters it’s easy to make a mistake you can’t undo.

Two copies in two places

One copy risks a single event taking everything: a flood, a fire, a burglary, a house move. Two copies in the same flat is the same risk multiplied by two.

A rule that’s enough for most people: the first copy at home, in a place only your closest person knows about. The second in another building: with a trusted relative, in a bank deposit box or in a locked office cupboard. A good place meets three conditions: it’s dry, it’s hard to discover, and it will be reachable when you’re gone.

The last condition is the one most often missed. A seed in a safe whose code only the owner knows is safe from the family and useless to the family. We cover this at more length in the guide family access instructions: what to include.

The person holding the second copy doesn’t need to know what it is. You can say it’s a document in case something happens. If you want one copy alone not to open the wallet, consider a passphrase or a 2-of-3 setup, covered below.

The choice of place is worth some thought. A cellar is damp, an attic heats up in summer, and by a window paper fades in the sun. The kitchen and bathroom are out because of water. A bedroom wardrobe is drier, but it’s the first place a burglar checks. For a copy kept by someone else, a locked cupboard or a deposit box that no random visitor looks into works best.

What not to do

The mistakes below repeat most often, and each of them means the copy has stopped being private.

1. A photo on your phone. Photos go automatically to the cloud, to backups and to apps with gallery permissions.
2. A note in an app, a document in the cloud, a file on the desktop. Trezor explicitly advises never keeping the backup digitally, because digital copies can be made without the owner’s knowledge.
3. A password manager. It’s protected by one master password and works online. A seed isn’t an account password. It’s access to your wealth.
4. An email to yourself or to your family. The mailbox is the first place burglars search.
5. Reading the words aloud with a phone or voice assistant switched on.
6. Typing the seed into a site or app “to check it”. A seed is typed only into the wallet device or the manufacturer’s software, and only when restoring.
7. Giving the seed to anyone who is “helping”. No support agent needs your words, and we don’t want to see them either.

If you’ve already done one of these, assume the seed is compromised. Create a new wallet and move the funds.

Keep the passphrase separate

A passphrase, or the 25th word, is an extra password that together with the seed defines the wallet. Under BIP39, with a different passphrase the same words open a different, valid wallet. If you use one, the rule is simple: don’t store it with the seed. The whole point is that finding the sheet with the words isn’t enough to withdraw.

Two traps. A passphrase has no checksum, so a typo opens a different, empty wallet and nothing warns you. And it must be available to the person who will use it after you. The full description is in the guide passphrase and the 25th word. If you want to split the seed itself into shares, see Shamir and SLIP39.

How to check the backup

You check a backup the way it will be used in an emergency: without the original device.

1. Before you send the first funds to the wallet, write down the first address the wallet shows.
2. Reset the device to factory settings or use a second device from the same manufacturer.
3. Choose the option to restore from a seed and type the words from the backup, not from memory.
4. Add the passphrase, if you use one.
5. Compare the first address with the one you wrote down. If the address matches, the backup is good.
6. If it doesn’t match, don’t send funds. Go back to step 3 and check every word, the order and the passphrase.

Some manufacturers build a backup check into the device that works without a reset. Check your model’s documentation for how it works and what exactly it confirms. Restoring on a reset device is more reliable, because it goes through the whole path your family will use.

For larger amounts, repeat the test once a year. Paper ages and software changes. In our care service we do this together with you.

How to check a steel backup

A steel plate needs a separate check, because stamping letters is the one step where you can’t fix a mistake with an eraser. Do it without typing the words into a computer.

1. Before you start stamping, have a paper backup ready that has passed a full restore test on a device.
2. After stamping, read the plate word by word and compare it with the paper copy, ideally with a second person reading one of them aloud in an empty room, with phones off.
3. Check the position numbers and the order, not just the words. For systems where only the first letters of words are stamped, make sure you know the rule for rebuilding them and that it’s written down separately from the plate, without the words.
4. Restore the wallet on a reset device, typing the words on the device from the plate, not from the paper. That’s the final check, and nothing goes into a computer.
5. Only after this test destroy any spare working notes and put the plate in its place.

If the plate fails the test, stamp a new one. Don’t correct the old one blindly.

Unusual situations

What if the seed wasn’t generated by your device? If you got the words from a seller or they were on a card in the box, don’t use them. A wallet must always generate a new seed at first start-up.

What if you have several wallets? Each has its own seed and its own backup. Label the sheets briefly and neutrally, for example “A” and “B”, and keep the description of what is what in a separate document with no words in it.

What if the backup is partly illegible? Call the manufacturer or write to us before trying to guess. Don’t type incomplete words into online tools.

What next

If you’re not sure your backup would survive a flood, or whether anyone besides you knows where it is, the quickest way to find out is a check-up: an hour’s online conversation, after which you get a list of risks, most urgent first. We never see your seed. We’ve collected the typical mistakes in the guide common crypto security mistakes.