Standard deviations for lake breakup dates were calculated for all lakes in Canada with reasonably long breakup records and for five lakes in Wisconsin with long‐term records. Standard deviations were about 13 days for coastal lakes and 7–11 days for continental lakes. The accuracy of the melting degree day method of predicting breakup dates were investigated for 12 of these lakes; standard deviations ranged from 3.3–8.0 days. Regression equations for predicting breakup dates were developed from past breakup and air temperature records for the 12 lakes; standard errors ranged from 1.6–4.3 days. General forecast guidelines were developed for application to lakes with limited breakup records. The equations and forecast guidelines are suitable only for continental lakes where wind and river inflow effects are not dominant.