This study was conducted to identify areas showing lower agroclimatological risk for corn associated to water deficit, in the State of Rio Grande do Sul, Brazil. The investigation was based on Corn Crop Agroclimate Zoning by Seeding Dates, in the State of Rio Grande do Sul. A Complementary Risk Index (CRI) was applied to areas suitable for corn determined in the agroclimate zoning. The purpose of such index is to detect those periods showing lower risk of occurring water deficit. CRI is based upon the interaction between water availability and critical development period of corn, as the main factor determining economic yield of corn in the state. The module Sarrazon was used in calculating daily water balance. Water balance simulations were carried out for corn, for early and normal varieties, considering the seeding dates on 5, 15, and 25 of each month. The main variable for the zoning was de ISNA (Crop Water Requirement Index) of the third development period (flowering-grain filling). The values of ISNA were calculated for a minimun frequency of 80% and then plotted on Spring v.3.4. Three categories were used: desirable (ISNA > 0.55), intermidate (ISNA between 0.45 and 0.55) and undesirable (ISNA < 0.45). The recomended sowing periods were stablished based on areas delimited by desirable ISNA values.