A method for determining daily weight values and store closure coefficients for use in forecasting daily sales patterns for retail products. The method uses historical daily demand data for a product to calculate a daily weight value for the product for each day of the week, each daily weight value representing the ratio of the historical daily demand for a corresponding day of the week to a total of the historical daily demands for the entire week. A daily demand forecast for each day of a forthcoming week is determined by applying the daily weight values to a predetermined weekly demand forecast for the forthcoming week. Historical demand data for weeks including holidays or store closures is used to calculate store closure coefficients, representing the ratio of the historical daily demand for days immediately preceding and following a store closure, to the historical demand for a corresponding day during a regular, non-holiday, week. The store closure coefficients are applied to the daily demand forecasts for days immediately preceding and following store closures or holidays to adjust the daily forecasts to accommodate changes in customer buying patterns resulting from the store closures.