Balanced diets are essential for horses to maintain health and obtain their performance. Recommendations regarding the daily nutrient supply are reviewed and published by the German Society of Nutrition Physiology (GfE) or the US American National Research Council (NRC). To meet the recommended daily mineral supply, horse owners, veterinarians and animal nutritionists rely on the mineral concentrations in feed supplements as declared by the feed producers. The objective of this study was to compare declared and analysed mineral concentrations in 19 commercial feed supplements. The minerals calcium, phosphorus, magnesium, sodium, potassium, iron, copper, manganese and zinc were investigated. Furthermore, the daily mineral intake from hay and feed supplements was compared to the recommendations by GfE. Nineteen, randomly chosen, commercial feed supplements distributed as mineral supplements for resting horses were considered in this study. Phosphorous concentrations were obtained via the vanadat-molybdat-methode, while calcium, magnesium, sodium, potassium, iron, copper, manganese, and zinc concentrations were measured by atomic absorptions spectroscopy (AAS). The analysed values were compared to the concentrations as declared by the feed producer. Tolerance levels were then applied as specified by the Regulation (EC) No 767/2009. Here, the latest updates by the commission regulation (EU) 2017/2279 were considered. Mineral concentrations in hay from Berlin-Brandenburg, Germany, from the year 2018 were obtained as described. A diet based on 1.5 kg hay/100 kg body weight (BW)/day and feed supplements fed according to producer recommendations was calculated for a horse with 500 kg BW. From this theoretical diet, the mineral supply was compared to recommendations by the GfE. In all 19 analysed feed supplements, deviations from the declared values were observed. These deviations both exceeded and fell below the legal tolerance margins in two or more minerals per sample. All examined feed samples revealed iron concentrations exceeding the declared content, also having the highest content of 1355 % above the declared concentration in one sample. The lowest concentration compared to the declared values was observed for copper, being 71 % lower than declared in one of the examined samples. The average deviations between analysed and declared values were 14 % (calcium), 19 % (phosphorous), 17 % (magnesium and sodium), 300 % (iron), 166 % (copper), 23 % (manganese) and 66 % (zinc). The calcium : phosphorous ratio reached from 1.5 : 1 to 6 : 1, when considering the analysed values. Phosphorous, copper, manganese and zinc concentrations did not meet the recommended daily intake when a ratio based on hay as the singular mineral supply was evaluated. Adding mineral supplements according to manufacturer’s recommendations to the daily ratio for a 500 kg horse, the recommended daily mineral intake was met for phosphorous, and manganese, but not for copper and zinc. Here, only 3 and 7 feed supplements, respectively, could balance the ratio according to the GfE recommendations. Accordingly, the copper supply reached 44–117 % of the recommended intake, while zinc was supplied at 61–158 % of the recommended intake. The remaining daily mineral intake recommendations were met by 244 % (Ca), 129 % (P), 296 % (Mg), 412 % (Na), 557 % (K), 273 % (Fe), and 157 % (Mn), on an average. In conclusion deviations between analysed and declared mineral concentrations could be observed in all 19 investigated feed supplements. Still, nutritional problems are not expected to occur except for zinc and copper, which revealed a substantial undersupply.