How Long Should a Password Be? NIST’s 2025 Rules Explained
For years, sites forced us to add a capital letter, a number and a symbol, and to change passwords every 90 days. The US National Institute of Standards and Technology now says those rules do more harm than good. Here is what its 2025 guidance actually requires.
What NIST SP 800-63B-4 says
| Topic | Requirement for services |
|---|---|
| Minimum length | 15 characters when a password is the only factor; at least 8 when it is used with multi-factor authentication |
| Maximum length | Should allow at least 64 characters |
| Composition rules | Must not require mixtures such as “one uppercase, one symbol” |
| Periodic changes | Must not force changes on a schedule — only when there is evidence of compromise |
| Blocklist | Must reject commonly used, expected or compromised passwords |
| Password managers | Must allow password managers and autofill; should allow pasting |
| Characters | Should accept spaces and Unicode |
Why length beats complexity
Each random character adds possibilities. A random password drawn from the 94 printable ASCII symbols gains about 6.6 bits of entropy per character; a random lowercase letter about 4.7 bits. So a 16-character random lowercase password (about 75 bits) is stronger than an 8-character “complex” one (about 52 bits) — and much easier to type. Human-chosen passwords are far weaker than these numbers, because people pick patterns; that is why randomness matters more than rules.
What you should do
- Use a password manager and let it generate a unique random password for every site.
- For the few passwords you must remember (the manager’s main password, your computer), use a passphrase of several random words.
- Turn on multi-factor authentication wherever it is offered.
- Change a password when a service reports a breach — not on a calendar.
Our Password Generator creates random passwords and passphrases with your browser’s cryptographic random number generator and shows the strength in bits. The strength checker estimates how guessable a password is; its optional breach check sends only the first five characters of the password’s SHA-1 hash (k-anonymity), never the password.