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A/B Testing Password Strength (Annual) Calculator

Compare two password designs by estimating their brute-force search space, annual compromise likelihood, and expected cracking time.

Your Details

Overview

Use this A/B password strength calculator to compare two password designs using their length, possible character set, and an assumed attacker guessing rate. It estimates each design's theoretical search space, annual brute-force compromise likelihood, and average exhaustive-search time.

How it works

For each design, the calculator estimates the number of possible passwords as character set size raised to password length. It then divides an attacker's annual guess budget by that search space to estimate the chance that a uniformly random password could be found by brute force within a year. The expected crack time assumes, on average, that the correct password is found halfway through all possible combinations. These estimates are most useful for genuinely random passwords; human-created passwords often have much less practical resistance than their theoretical character count suggests.

How to use this calculator

  1. 1Enter the length of password design A.
  2. 2Enter the number of characters that could be used in password A.
  3. 3Enter the length and character set size for password design B.
  4. 4Set an effective attacker guessing rate that reflects the system's protections.
  5. 5Compare the annual compromise estimates and relative search-space result.

Example Calculation

Password A length

12

Password A character set size

94

Password B length

16

Password B character set size

94

Attacker guesses per second

1000

Password B annual compromise likelihood

0.000000%

With the same 94-character set, the 16-character design has a vastly larger search space than the 12-character design, so its estimated annual brute-force compromise likelihood is much lower at the same guessing rate.

Frequently asked questions

What does character set size mean?

It is the number of characters that could appear in each position. For example, lowercase English letters have a size of 26, while letters, digits, and common symbols may total about 94 characters.

Does a longer password always improve brute-force resistance?

For randomly generated passwords, adding characters increases the number of possible combinations and generally improves resistance substantially. Predictable additions, such as a common word or repeated pattern, may not provide the same benefit.

Why do I need to enter an attacker guess rate?

Guessing speed depends heavily on whether the attack is online or offline, the password hashing method, rate limits, account lockouts, and available computing resources. Entering a rate makes the estimate adaptable to those conditions.

Does this calculator test my actual password?

No. It compares password designs using length and character-set assumptions only. Do not enter a real password into public tools or share it with anyone.

Why can a theoretically strong password still be risky?

A password can be exposed through phishing, malware, data breaches, reuse on another site, or predictable construction. Unique random passwords and multi-factor authentication reduce several of these risks.

What does expected crack time mean?

It is an average exhaustive-search estimate. If guesses are tried without knowing the password, the correct value is expected to be found about halfway through the possible combinations, not necessarily at the end.

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Assumptions and warnings

Assumptions

  • Each password is assumed to be randomly generated from its stated character set rather than based on words, patterns, or personal information.
  • The attacker is assumed to make distinct guesses continuously for 365 days at the entered effective rate.
  • The annual compromise likelihood is capped at 100% and represents an exhaustive brute-force model.
  • Expected crack time uses the average case, where the correct password is found halfway through the possible search space.
  • The entered guess rate should reflect practical controls such as hashing cost, rate limiting, lockouts, and multi-factor authentication.

Warnings

  • This calculator is an estimate only; real-world password attacks can exploit reused, leaked, predictable, or phishing-obtained passwords.
  • Use unique passwords, a password manager, and multi-factor authentication where available.