The BoneCalc app is designed for the calculation of Z-scores and percentiles for bone mineral content (BMC) and areal bone mineral density (aBMD) for children under 20 years of age, as measured by dual-energy X-ray absorptiometry (DXA), for the following sites: whole-body subtotal (total-body-less-head), total hip, femoral neck, lumbar spine, distal ⅓ radius and ultradistal radius. Separate race-specific (Black and non-Black) and race-neutral calculations are available by age and sex. Height-Z–adjusted Z-scores for these measures are also calculated. The BMC and aBMD data are derived from the CHOP Bone Mineral Density in Childhood Study: race-specific for ages 5–20 [Zemel B et al., J Clin Endocrinol Metab 2011;96(10):3160–3169]; race-specific for ages 1–5 [Kalkwarf HJ et al., J Clin Endocrinol Metab 2022;107(9):e3887–e3900]; and race-neutral ages 5–20 [Zemel BS et al., J Clin Endocrinol Metab 2025;110(11):3034–3048]. Calculations are also available for lumbar-spine bone mineral apparent density (BMAD) for children 5–20 years of age: race-specific [Kindler JM et al. J Clin Endocrinol Metab 2019;104(4):1283–1292] and race-neutral [Zemel BS et al., J Clin Endocrinol Metab 2025;110(11):3034–3048].