Calcium balance refers to the state of the body stores of calcium at equilibrium over some extended time period (usually days, weeks, or months). It results from the net effects of intestinal absorption and renal, intestinal, and sweat gland excretion on bone calcium, the dominant calcium pool. Bone balance changes throughout the normal lifespan, depending on relative rates of bone formation and resorption. Children are in positive bone balance (formation > resorption), which ensures healthy skeletal growth. Healthy young adults are in neutral bone balance (formation = resorption) and have achieved peak bone mass. Elderly individuals are typically in negative bone balance (formation < resorption), which leads to age-related bone loss. Factors that promote positive bone balance in adults include exercise, anabolic and anti-resorptive drugs, and conditions that promote bone formation over bone resorption (e.g., “hungry bone” syndrome, osteoblastic prostate cancer).