A system that permits authentication based on a partial password, in which a risk score is assigned to an authentication request, and a minimum partial password size is generated based on the risk score. User-entered password characters are compared to one or more partial passwords having lengths equal to or greater than the minimum partial password size. If a match is found, the user is authenticated. A password similarity threshold for the request may also be generated based on the risk score, indicating a minimum level of similarity required between the user-entered password characters and the characters in a partial password, in order for there to be a match. When the user-entered password characters match a partial password, and the requesting user is authenticated, the system may stop inputting user-entered password characters, and/or transmitting the user-entered password characters to a server computer.