The objective of this work was to synthesise and analyse the methodologies and the biological aspects of the costs calculation in ruminants in Slovakia. 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). 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. In suckler cows is a live-born calf the main product and manure is the by-product. 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. Subtraction, allocation and combined calculation methods of costs are the most used in breeding of ruminants. It is recommended to consider specific breeding conditions and objective calculation of costs for the relevant category, when picking out the method of calculation.