The eggs are normally laid at intervals of three days and are incubated only by the female. Laying generally begins in late winter but may be later in the year in colder habitats. During the incubation period, the female is brought food at the nest by her mate. A single clutch of white eggs is laid; each egg can measure from long by in width, and will usually weigh about . In Central Europe, eggs average , and in Siberia, eggs average . Their eggs are only slightly larger than those of snowy owls and the nominate subspecies of great horned owl, while similar in size to those of spot-bellied eagle-owls and Blakiston's fish owls. The Eurasian eagle-owl’s eggs are noticeably larger than those of Indian eagle-owl and pharaoh eagle-owls. Usually clutch size is one or two, rarely three or four, and exceptionally to six. The average number of eggs laid varies with latitude in Europe. Clutch size ranges from 2.02–2.14 in Spain and the massifs of France, and 1.82 to 1.89 in central Europe and the eastern Alps; in Sweden and Finland, the mean clutch size is 1.56 and 1.87, respectively. While variation based on climate is not unusual for different wide-ranging palearctic species, the higher clutch size of western Mediterranean eagle-owls is also probably driven by the presence of lagomorphs in the diet, which provide high nutritional value than most other regular prey. The average clutch size, attributed as 2.7, was the lowest of any European owl per one study. One species was attributed with an even lower clutch size in North America, the great grey owl with a mean of 2.6, but the mean clutch size was much higher for the same species in Europe, at 4.05.