This dataset contains daily reference evapotranspiration (ETo) values calculated using the FAO-56 Penman-Monteith method for the area of Lake Chimaditida, Western Macedonia, Greece. The dataset covers 3,103 daily records from September 1, 2016 to February 28, 2025. ETo values are expressed in mm/day and range from 0.17 to 7.95 mm/day, with a long-term daily mean of 2.58 mm/day. The Penman-Monteith equation, as standardised by the Food and Agriculture Organization of the United Nations in FAO Irrigation and Drainage Paper No. 56, is the internationally recommended method for estimating reference evapotranspiration. The dataset is relevant for water balance studies, irrigation planning, and hydrological modelling in the broader Chimaditida wetland area.