Total seasonal rainfall being mostly sufficient during the rainfed kharif rice- growing period in the Purulia district of West Bengal, the crop is subjected to frequent water stress due to its uneven distribution. To assess the effective part of the total rainfall for kharif rice a daily rainwater balance approach has been followed to estimate effective rainfall (ER) against a given total rainfall (TR) during July, August and September and its contribution to rice yield in the Purulia district Twenty years of historical rainfall database across 8 different locations along with 13 years of historical rice yield data were analysed. ER for rice varied from 63-66% during these three rice- growing months. Coefficient of variability of monthly TR was much higher than the ER for the same period. ER during August showed maximum degree of association with rice yield (r = 0.78*). Degree of association between ER and yield has been higher than that with TR and thus ER is a better predictor of rice yield than TR. Three different multiple regression equations were tried using components of this rainwater balance to predict rice yield; one equation involving ER corresponding to July, August and September is recommended for its maximum goodness of fit.