Ideally seed should be replaced every year for hybrids and every three to four years for non-hybrids. However, in practice seed is replaced less often especially in case of open pollinated crops. As a consequence, seed replacement rates are lower than recommended for different crop varieties. As adequate information is not available on replacement schedules followed by farmers, how to compute actual replacement rates? One simple method is to take the ratio of quality seed of a crop produced during the year to the total seed needed to cover the entire area under the crop. This method does not consider the crop produce from F2, F3 and F4 generations distributed as seed among the fellow farmers. This paper presents an alternative model which considers such lateral distribution of seed from successive generations of a variety. The model gives more precise estimates of replacement rates for better planning of seed production activity and is thus named as "improved model".