PIN Strength Calculator

blind guessing: P = attempts ÷ 10^length. Informed guessing: P = common-PIN share + (1 − share) × attempts ÷ 10^length. A four-digit PIN has 10,000 combinations and 13.29 bits, so three blind guesses succeed 0.03 % of the time. Human choice destroys that: leaked PIN datasets show 1234 alone accounts for about 10 % of PINs, and the top three cover roughly 18.6 %, so an attacker who starts there beats the blind figure by nearly a thousandfold.

PINs guard phones, SIMs and bank cards on a three-attempt budget, and the gap between the theoretical and the observed guess rate is the entire argument for blacklisting common values.

This calculator takes 4 inputs: PIN length, Attempts allowed, Attacker tries common PINs first, Share of users covered by those guesses. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.

Each digit adds 3.32 bits and multiplies the keyspace by ten, so a six-digit PIN drops blind guessing to 0.0003 % for three attempts. It does nothing about predictable choices — birth years dominate six-digit PINs the way 1234 dominates four-digit ones.

A blacklist of the top few hundred PINs, combined with a hard attempt limit. That removes the entire informed-guessing advantage and leaves the attacker with the blind probability shown here.