What is a seed phrase? (And how people lose everything)
A seed phrase (or recovery phrase) is a list of 12 or 24 ordinary words that encodes the master private key to a crypto wallet. Whoever knows those words controls the funds — from any device, anywhere, with no password reset and no fraud department to call. Lose the phrase and the device, and the crypto is gone; leak the phrase, and it will be stolen. Almost every catastrophic self-custody loss traces back to the same two mistakes: storing the phrase digitally (photos, cloud notes, email) where malware finds it, or typing it into a website because something claiming to be "support" or a "wallet validation" asked. Paper or steel, offline, never shared, never typed — that's the whole discipline.
What the words actually are
When a wallet is created, it generates a large random number — the master key from which every address and private key in the wallet is derived. Because humans are terrible at transcribing long numbers, wallets encode that number as a sequence of words drawn from a fixed standardised list. The words are just a human-friendly spelling of the key: same words, same order, same wallet — on any compatible device, forever.
This is why a broken or lost device is a non-event when the phrase is safe, and why the phrase is everything: it doesn't unlock your wallet, it IS your wallet.
How seed phrases actually get stolen
- Phishing: a site, popup or "support agent" asks you to "validate", "sync" or "restore" your wallet by entering the phrase. No legitimate service ever asks — this is always theft
- Digital storage: a screenshot in your camera roll, a note in the cloud, an email to yourself — one compromised account or infected device later, gone
- Fake wallet apps and tampered devices that show you a phrase an attacker already knows
- Physical discovery: the note in the desk drawer, found by the wrong person
Storing one properly
Write the words on paper, by hand, at setup — the phrase should never touch a keyboard, camera or clipboard. Store it somewhere secure at home (and ideally a second copy in a separate secure location — a safe, or with trusted family). For serious holdings, stamped steel plates survive the fires and floods paper doesn't. Advanced users add an optional passphrase — a "25th word" — so even a discovered sheet of paper isn't enough; just understand that a forgotten passphrase is as fatal as a lost phrase.
And think about inheritance: a phrase nobody else can ever find is also a phrase your family can never find. Sealed instructions in a will-adjacent place solve a problem most people prefer not to think about.
Ad · Steel backup plates are sold direct by the wallet manufacturers — for example the Billfodl on Ledger's official shop (affiliate link).
The UK tax angle on lost access
Losing your seed phrase is not automatically a tax loss. HMRC still regards you as owning the coins — they exist on-chain; you've lost the key, not the asset. In narrow circumstances, where you can evidence there's no realistic prospect of ever recovering access, a negligible value claim may be possible, but it's fact-specific and worth professional advice. Prevention is dramatically cheaper than the tax argument.
Buying a hardware wallet? Buy direct.
Ad · AffiliateWhichever brand you choose, order from the manufacturer’s own store — never marketplace resellers, where tampered devices are a documented scam. Buying through the Ledger link below supports this free site.
Affiliate disclosure: the Ledger link is an affiliate link — if you buy through it we may earn a commission at no extra cost to you. The Trezor link is not an affiliate link. This is an advertisement, not tailored advice; both are reputable manufacturers.
Run your own numbers — free
Our calculator applies these rules to your transactions and shows the full working for every disposal — same-day, 30-day and Section 104 matching, per tax year.
Open the calculator →Frequently asked questions
Can I store my seed phrase in a password manager?
Most security guidance says no for meaningful sums — it reintroduces exactly the online, phishable attack surface the phrase is meant to escape. Offline media only.
Someone asked for my phrase to 'verify my wallet'. Legit?
No — 100% a scam, every time, regardless of how official it looks. No wallet company, exchange or support team ever needs your words.
I've lost access to a wallet — can I claim a tax loss?
Not automatically. Lost keys aren't a disposal, and HMRC treats you as still owning the asset. A negligible value claim is sometimes possible with strong evidence — take advice before relying on it.
Sources & methodology
Tool v0.2.0 · sources last checked 6 July 2026. This guide is general information, not tax or financial advice — verify your position with a qualified professional before filing.