In recent years, the knowledge on feeding of cold-water corals has increased considerably. However, little is known about their energy gains from feeding and the resulting energy balance. A complete energy budget is presented for cold-water coral (CWC) Desmophyllum dianthus from Patagonian Comau fjord, recorded under conditions close to in situ. Three feeding treatments were applied: (I) corals fed with living, freshly-collected fjord zooplankton, (II) corals fed with krill and zooplankton and (III) corals starved for four days. Ambient zooplankton concentrations were chosen to attain the previously assessed daily prey capture rates of D. dianthus in Comau fjord. At first, ingestion of zooplankton-derived organic carbon and nitrogen was determined in open-cell incubations. Subsequent closed-cell incubations allowed the measurement of the budget parameters respiration, ammonium excretion and organic matter release in terms of particulate and dissolved organic matter (POM and DOM). Daily somatic growth rates were derived from respective skeletal growth rates determined via the buoyancy weight technique. Feeding significantly increased organic matter release and respiration for maximally 24 hours. Metabolic activity was lower than in Mediterranean D. dianthus, but higher than in Lophelia pertusa. Starved corals showed a trend to take up DOC. In spite of relatively low metabolic rates compared to its Mediterranean counterpart, and high assimilation efficiencies (71.5 - 93.2 %), feeding on fjord zooplankton alone (I) was not sufficient to sustain Chilean D. dianthus’ metabolic energy demand. Beforehand determined daily prey capture rates were probably underestimated due to neglecting the increased zooplankton availability at night. Krill+zooplankton-fed corals (II) were able to retain 56.1 % of their ingested energy after subtraction of losses in terms of POM (7.5 %) and respiration (36.4 %). This remainder called scope for growth (SfG) was far larger than assessed energy flux into somatic growth, only accounting for 8.4 % of the ingested energy. Based on the present results, high minimum zooplankton food amounts of 477 to 614 zooplankton individuals per day, or regular feeding on larger prey items such as krill are suggested for D. dianthus. Lower food availability in winter could be partly compensated by uptake of DOM. Seasonally varying allocation of energy to the respective prevailing biological processes such as reproduction may support optimal utilization of energy resources. High assimilation efficiencies, in line with fast digestion of probably less than 24 h, emphasize D. dianthus’ potential of effective energy assimilation and probably provide an explanation for the CWC’s high abundance and dominance over large areas in the Patagonian fjord system.