A/B Testing Password Strength Calculator
Compare two password designs using estimated entropy, character variety, and a predictability adjustment.
Overview
Use this A/B Testing Password Strength Calculator to compare two password designs without entering the passwords themselves. Add each design's length, likely character variety, and an adjustment for predictable patterns to estimate which option has more effective entropy.
How it works
The calculator starts with an estimated number of bits per character based on the selected character variety. It multiplies this figure by password length, then reduces the result by the predictability penalty. This does not test a real password or simulate every attack method. Instead, it provides a consistent way to compare two proposed password structures: more effective entropy generally means a larger search space for a guessing attack.
How to use this calculator
- 1Enter the length of Password A without typing the password itself.
- 2Choose the character variety that best matches Password A.
- 3Apply a predictability penalty for words, patterns, dates, or familiar information.
- 4Repeat the same steps for Password B.
- 5Compare the entropy estimates and the difference between the two options.
Example Calculation
Password A length
12
Password A character variety
5.95
Password A predictability penalty
20%
Password B length
16
Password B character variety
6.55
Password B predictability penalty
5%
Password B estimated entropy
99.6 bits
Password A is estimated at about 57.1 bits, while Password B is estimated at about 99.6 bits. Password B has roughly 42.4 more estimated bits of entropy.
Frequently asked questions
What does an A/B password strength comparison measure?
It compares two password designs using estimated effective entropy. The comparison accounts for length, character variety, and an adjustment for predictable content.
Should I enter my actual password?
No. Enter only non-sensitive design details such as the length, character types, and an estimate of how predictable the structure is.
What is the predictability penalty?
It is a percentage reduction for features that can make a password easier to guess, such as dictionary words, keyboard runs, dates, repeated characters, or personal references.
Does adding symbols always make a password much stronger?
Symbols can increase the possible character pool, but a longer random password or passphrase can also be strong. Predictable substitutions and familiar patterns may reduce the practical benefit.
What does a positive entropy difference mean?
A positive difference means Password B has a higher estimated entropy than Password A. A negative difference means Password A has the higher estimate.
Is estimated entropy a guarantee of password security?
No. Actual security also depends on uniqueness, account protections, password storage practices, phishing risk, and whether the password has been exposed elsewhere.
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Assumptions and warnings
Assumptions
- The calculator estimates password design strength from length, character variety, and a user-selected predictability adjustment.
- Character variety values are approximations of the possible character pool and do not inspect an actual password.
- A predictability penalty is intended to reflect common words, keyboard patterns, dates, repeated sequences, and personally related content.
- Results are comparative estimates rather than a measurement of a password's real-world security.
Warnings
- Do not enter a real, current, or sensitive password into this calculator.
- Password strength alone cannot protect an account if passwords are reused, stolen through phishing, or exposed in a data breach.
- Use unique passwords and multi-factor authentication where available.