Credential Stuffing Success Rate Calculator

Credential Stuffing Success Rate Calculator

Credential stuffing attacks automate login attempts using username/password pairs leaked from unrelated data breaches, betting on the fact that many people reuse passwords across multiple sites. This calculator estimates how many accounts could realistically be compromised at scale.

Formula

1. Reused Credentials = Credentials Tested x Reuse Rate%
2. Successful Logins = Reused Credentials x Login Success Rate%

Example

1,000,000 leaked credentials tested, 15% password reuse rate, 2% login success rate among reused credentials:

Reused = 1,000,000 x 15% = 150,000 → Successful Logins = 150,000 x 2% = 3,000 compromised accounts

Why Small Percentages Add Up to Big Numbers

Even a login success rate as low as 2% sounds negligible in isolation, but applied against a leaked list of a million credentials it still yields thousands of compromised accounts - and real-world leaked credential databases number in the billions of records. This scale is exactly why multi-factor authentication and unique, non-reused passwords are considered baseline defenses against credential stuffing, since neither depends on the target site itself ever being breached.