An attempt was made to estimate average calcium requirements for various age groups by gender. The factorial method that sums calcium accretion and endogenous losses modified by fractional absorption was used during growth and calcium intakes to achieve calcium balance was used for adults. These estimates exceed the current RDA for females aged 6-16 y and older than 30 y and for males aged 6-30 y. They also exceed current calcium intakes in the U.S. during adolescence for both sexes and for females above the age of 11 y. A number of factors influence calcium requirements with age. Requirements for calcium accretion is dominant until peak daily calcium retention during the adolescent growth spurt is achieved. The rate of calcium accretion with age varies widely, depending on the method of estimation. Urinary calcium losses increase until young adulthood. Contributions of endogenous fecal calcium and sweat calcium to obligatory calcium losses are largely unknown during growth. After growth ceases, calcium requirements increase with menopause, unless estrogen-treated, and with age as calcium absorption efficiency decreases. Data required to estimate calcium requirements during growth are insufficient to precisely define dietary requirements with age. Determining calcium intakes which optimize calcium retention, and therefore, bone mass as has been estimated by Matkovic and Heaney (1992) may be a sound approach. The requirements estimated by this approach will be difficult to achieve given current dietary intakes in the U.S.