Objective/context: This article analyzes the effects of the Chilean electoral reform on proportionality, focusing mainly on electoral pacts. Methodology: The research uses data of the election of the Chilean Chamber of Deputies of 2017, in order to calculate the effects of two variables on proportionality within the electoral pacts: party size and number of seats obtained. Moreover, it analyzes the strategies of small parties in order to maximize their gains. Conclusions: Proportionality within electoral pacts depends on the number of seats obtained and the size of the parties. Small parties that concentrate their candidacies in few districts and thereby use their economic resources more efficiently, can maximize their benefits within the pact. Originality: The article provides new evidence regarding the effects of electoral pacts on seat allocation in proportional systems by analyzing a case that has not been studied until now.