Work out your BIP39 seed with a coin
Flipping a coin 256 times gives you entropy that does not depend on trusting anyone else's generator. The one step you cannot do by hand is the checksum, a SHA-256 over those bits — that is what this calculator is for. Download it and run it on a machine with no network.
This page came off the internet. That is not "100% offline".
For a seed that will actually hold funds: download the file, take the machine off the network and open it from disk. Everything is computed in your browser and nothing leaves it — there is no analytics on this page — but that is something you should verify, not take on faith. Here, practise.
Length
256 flips
Type or paste the bits, or use the buttons. Spaces and line breaks are ignored.
0/256
Your seed
And inside the app…
Finzolio never touches your keys and never asks for them: it tracks what your Bitcoin is worth alongside the rest of your wealth, Spanish tax included. Custody stays yours, as it should.
Related tools
Start measuring your portfolio properly
Your portfolio, your dividends and your taxes, consolidated from day one. No card, no commitment.
No spam. Just one email the day we open, and you can unsubscribe any time.