Nowadays, waste management has become a serious concern of society due to increasing population growth rate and waste production. Despite efforts have been made to reduce the landfilling rate in Iran, a large amount of waste is still disposed of in landfills. Leachate generation is a major problem of landfills and, if not managed properly, it can cause significant threat to surface water and groundwater near to the landfill. Therefore, it is necessary to design a proper collection system to remove the leachate from landfill efficiently. Knowing the rate of leachate generation with reasonable accuracy is the critical input to design a landfill leachate collection system. In this study, a water balance method was used to estimate the amount of leachate produced in the Halgheh Darreh landfill of Karaj. In this model, we have considered a wide range of parameters that contribute to leachate generation in a landfill including rainfall, annual heat index, runoff, potential and actual evapotranspiration, the rate of leachate recirculation, evaporation from the surface of recirculation ponds, the amount of water used in gas production and also the initial moisture content of waste at the gate of landfill. The leachate generation rate was calculated for each month. In order to validate the results of the model, the actual leachate production was measured in December, January, February, March, April, May, June, and July. The comparison of the model estimates against the actual values measured at the site indicated an acceptable accuracy with a correlation coefficient (R) and the coefficient of determination (R2) equal to 0.966 and 0.933, respectively. Also, the root-mean-square error (RMSE) and mean absolute value of error percentage (MAPA) were 1328.27 and 9.17%, respectively, showing a small difference between the actual values and predicted values by the model. Also, the sensitivity analysis of the input parameters showed that the most important factor influencing the leachate generation is the moisture content of the incoming waste. The model developed in this study was a simple model and, with limited modification, it can be applied in other landfills located in arid regions of Iran.