This paper shows that regardless of how good the economic situation is, sooner or later certain difficulties will appear. Hence, the idea has emerged to give the analytical form to the logistic law based gradient measurement (synthetic measure) of selected financial data, which enables forecasting crises and economic downturns. The presented proposal of determining the economic cycle and the model of forecasting using the modified logistic function (log-logistic function) was tested with use of data regarding the Polish economy.