The study aimed to estimate the Irrigation Water Requirement and Irrigation scheduling of Carrot plant under Drip irrigation system at IPRC Gishari Farm located in Rwamagana District, Rwanda. Experimentally, the study covered the total area of 120 m x 64 m= 7680 m2 or 0.768ha of cropped land. The area of sub plots was 30 m x 16 m= 480 m2 or 0.048 ha of land. The Cropwat 8 computer packages was used to compute Reference evapotranspiration, Irrigation Water Requirement (IWR) and irrigation scheduling in drip irrigation installed for carrot production at the experimental site. The study findings showed that the monthly average mean of solar radiation was 34.9 MJ/m²/day while its range varies from 32.2 MJ/m²/day to 37.5 MJ/m²/day. It was found that also that the mean ETo from the experimental site is 5.94 mm/day. Its range varies from 5.43 mm/day to 6.47 mm/day. The total of rain fall and effective rain fall was found to be 1148.6mm and 962.6mm for the period of twelve months. It was found that the total irrigation water requirement for carrot production under drip irrigation for the season starting from 16 May to 19 August was found to be 273.2 mm while the Net Irrigation Water Requirement (NIWR) was found to be 3,557.3m3/ha which is very low compared to Gross Irrigation Water Requirement (GIWR). The GIWR from the experimental site was found to be 6,532.6m3/ha. The water deficit accrued in drip irrigation system was found to be 2,975.3 m3/ha. It was found that also the planting date of carrot started on 16 May of the year and the harvesting date was scheduled on 19 August and the total duration of the crop was 100 days. The moisture depletion pattern during the irrigation schedule varies from 32% to 66% with an average depletion of 54.5% for the whole cropping period. It is concluded that the total amount of water stored in carrot root zone is less than the total needed water and the crop cannot suffer from water deficit. For crop water requirement, it was also found that the total of rain fall was higher than effective rain fall stored in root zone for the period of twelve months and these implies higher Crop water need and as results Maximum potential yield for most irrigated carrot under drip trickle irrigation system in the study area has increased substantially during the irrigated plot.