Agricultural machinery is used not only to increase the labour productivity, but also to complete the any agricultural activities based on agricultural machinery usage on time. Mostly, farmers consider to achieve different operations according to available machine capacities. This scheduled idea may not be resulted with success all the time due to unexpected machine downtime resulting from several failures. If this fact does not take into account in planning stage, machine failures can cause serious stoppages which effect the production profitability in intensive operation period. To consider the negative effect of probable failures beforehand anyone should know about machine reliability. Researches on predicting and planning for downtime are important part of reliability studies of agricultural machinery. In this study, an estimation method was explained and a computer program was developed to calculate Weibull distribution parameters which is generally accepted statistical distribution as best-fitted to agricultural field. This program uses the minimum least square method for calculating the Weibull parameters. On the other hand, Monte-Carlo simulation method is included for predicting the time between failures and time to repair values.