Short answer: Yes, comfortably — but not for the reason people assume. Six digits give a one-in-a-million chance per guess, which sounds guessable. What makes it secure is the combination of a 30-second window and server-side rate limiting: an attacker gets a handful of attempts before being locked out, not a million. The security comes from the system around the code, not the code’s length.
The raw numbers
A six-digit code has 1,000,000 possible values, from 000000 to 999999. A single random guess has a 0.0001% chance of being right.
Put that way it sounds weak. A password with a million possibilities would be cracked instantly. The difference is that a password can be attacked offline, at billions of guesses per second, against a stolen hash. A TOTP code cannot — every attempt must go to the server, one at a time.
What actually protects it
1. The time window. Codes change every 30 seconds. Servers typically accept the current window plus one either side, giving roughly 90 seconds of validity. After that, a code is dead regardless of who has it.
2. Rate limiting. This is the real defence. Services allow perhaps 3 to 10 wrong codes before locking the attempt, requiring a delay, or triggering an alert. With five attempts per window, the probability of success is around 1 in 200,000 — and each failure is visible.
3. Password required first. The attacker needs a valid password before they even reach the code prompt. Two independent obstacles, not one.
4. Alerting. Repeated failures generate notifications. Sustained brute-forcing is loud.
Do the arithmetic and an attacker with a valid password, attempting continuously, would need an implausible amount of time and would trip every alarm on the way. It is not a viable attack, which is why nobody uses it.
Mechanics of the code itself: what is a TOTP code.
Why not eight digits, or ten?
Because the marginal security gain is close to zero and the usability cost is not.
Given rate limiting, six digits already reduce the attack to impracticality. Eight digits would make an already impractical attack more impractical, while making every login slower and more error-prone for billions of people. The standard permits longer codes, and hardly anyone uses them.
The exceptions are instructive: some enterprise hardware tokens use eight digits, and Steam uses five alphanumeric characters — which has a larger space than six digits, incidentally. Both are choices about their specific context, not corrections of a flaw.
Where the real weaknesses are
If you are worried about your 2FA, code length should be near the bottom of your list. In descending order of actual risk:
- You typing the code into a fake page. Real-time phishing relays it to the genuine site in under a second. Length is irrelevant — see can 2FA be hacked?
- You reading the code to someone. The most effective attack in existence — OTP scams.
- The secret key leaking. A screenshotted QR code hands over every future code permanently — what’s inside a 2FA QR code.
- Session theft. No code is requested at all — session hijacking.
- SIM swapping, if you are on SMS — SIM swap attacks. Mobile money services live entirely with this risk, so see how to secure a mobile wallet account.
- Weak rate limiting on a badly built site. This is the only case where digits would matter, and it is the site’s flaw, not the standard’s.
Every one of these bypasses the guessing problem entirely. Making codes longer would prevent none of them.
What about the secret behind the code?
A fair question, and the answer is reassuring. The secret key is typically 160 bits — around 2^160 possibilities. That is not brute-forceable by anyone, ever, with any foreseeable technology.
The six digits are a truncation of a hash of that secret and the current time. Seeing a code tells an attacker essentially nothing about the secret. So the weak-looking part is a disposable output, not the key itself.
The methods that remove the question
If code guessing worries you philosophically, the answer is not longer codes — it is not using codes.
Passkeys and security keys use challenge-response cryptography with no shared secret and nothing to type. There is no number to guess, intercept or be talked out of. See passkeys vs 2FA and phishing-resistant MFA.
That is the genuine upgrade path. Six digits are fine; zero digits are better.
Frequently asked questions
Could someone guess my code by luck?
In principle, once in about a million attempts — and they will be locked out long before. They would also need your password first.
Why do some services use 8-digit codes?
Mostly enterprise hardware tokens, where the usability cost is acceptable and policy demands a larger margin. It is a policy choice, not a security necessity.
Is a 4-digit PIN as safe?
No. 10,000 possibilities is meaningfully weaker, which is why PINs are used where physical possession is also required — a bank card, a phone in your hand. Context does the work there, and banks make much the same trade with codes — see why banks still use SMS 2FA.
Does the 30-second window make codes weaker?
Stronger. A short life limits exposure — a code glimpsed over your shoulder is worthless almost immediately. It is the reason TOTP replaced counter-based codes for most uses; see TOTP vs HOTP.
What if a site has no rate limiting?
Then its 2FA is genuinely weaker, and that is a site problem. Any reputable service limits attempts. It is not something you can inspect from outside, which is another argument for passkeys where offered.
Should I worry about quantum computing?
Not for TOTP. The concern applies to certain public-key cryptography, and the standards world is already migrating. The HMAC construction behind TOTP is not the vulnerable kind.
The bottom line
Six digits are enough because they are never faced alone: a password comes first, the window is 30 seconds, and the server stops guessing after a handful of attempts. The realistic threats to your 2FA are phishing, social engineering and a leaked setup key — none of which more digits would fix. If you want to remove the number entirely, that is what passkeys are for.
Curious how the codes are generated? Try our browser-based 2FA code generator, which computes them locally.