Agriculture in Benin mainly rainfed has experienced a disruption in relation to the agricultural calendar due to the effects of climate variability. The objective of this work is to contribute to the improvement of cotton yield by an appropriate choice of the sowing period in the Municipality of Banikoara. To achieve this, climatic data covering the period from 1981 to 2015 were collected and processed using different software (Excel spreadsheet, Khronostat).It emerges from this work that there is a strong variation in rains and temperatures during the period 1981 to 2015 with a downward trend in the rainy season. Thus, the favorable periods for cotton cultivation are those where the start of the cycle is between the periods of June 10 to 30. Regarding the sowing date of June 15, a significant yield of 1987.5 kg / ha was recorded. At the same date, a significant improvement in the phenological parameters was observed, the largest size of the cotton plant being estimated at 67.25 cm and the diameter of the pod is 2.85 cm.As a result, improving cotton yield in the study area must go through the reorganization of the cropping calendar.