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PIN Strength Calculator

Score a numeric PIN against both blind guessing and an attacker who tries the most common PINs first.

About PIN Strength Calculator

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.

Formula

PIN Strength

blind guessing: P = attempts ÷ 10^length. Informed guessing: P = common-PIN share + (1 − share) × attempts ÷ 10^length.

10^length
10,000 for a four-digit PIN
common-PIN share
Fraction of real users whose PIN is among the attacker's first guesses

Worked example

With the default values below, PIN Strength Calculator returns Chance the PIN Is Guessed of 18.624%. Change any input above and every figure here is recalculated in your browser.

Inputs used

PIN lengthaccepts 3–12 digits
4 digits
Attempts allowedaccepts 1–1,000 attempts
3 attempts
Attacker tries common PINs first
Yes
Share of users covered by those guessesaccepts 0–100 %
18.6 %

Results

Chance the PIN Is Guessed
18.624%
Possible PINs
10,000 PINs
PIN Entropy
13.29 bits
Chance Against a Truly Random PIN
0.0300%
Risk Band
Medium

Step by step

  1. 1Values used
  2. 2PIN Strength
  3. 3Chance the PIN Is Guessed= 18.624
  4. 4Possible PINs= 10,000 PINs
  5. 5PIN Entropy= 13.29 bits
  6. 6Chance Against a Truly Random PIN= 0.0300
  7. 7Risk Band= Medium

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is PIN Strength calculated?

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.

Why does PIN Strength matter?

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.

What values do I need to enter?

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.

Does adding digits help?

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.

What is the single most effective PIN control?

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.

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