The objective of this work was to synthesise and analyse the methodologies and the biological aspects of the costs calculation in ruminants in Slovakia. According to literature, the account classification of cost items is most often considered for construction of costing formula. The costs are mostly divided into fixed (costs independent from volume of herd’s production) and variable ones (costs connected with improvement of breeding conditions). Cost for feeds and beddings, labour costs, other direct costs and depreciations were found as the most important cost items in ruminants. It can be assumed that including the depreciations into costs of the basic herd takes into consideration the real costs simultaneously invested into raising of young animals in the given period. Costs are calculated for the unit of the main and by-products and their classification is influenced mainly by the type of livestock and production system. In dairy cows is usually milk defined as the main product, and byproducts are live born calf and manure. The base calculation unit is kilogram of milk (basic herd of cows) and kilogram of gain and kilogram of live weight (young breeding cattle). In suckler cows is a live-born calf the main product and manure is the by-product. The costs are mostly calculated per suckler cow, live-born calf and per kilogram of live weight of weaned calf. Similar division of products into main and by-products is also in cost calculation for sheep categories. The difference is that clotted cheese is also considered as the main product of basic herd in dairy sheep and greasy wool as the by-products in all categories. Definition of the base calculation units in sheep categories followed the mentioned classification.