In this paper we contribute to literature on human capital formation by investigating age references on early-modern portraits from the Low Countries. We use the very popular aetatis formulae to estimate to what degree sitters to portraits were able to give their age in an accurate way. This approach allows us to estimate the numeracy of single men and women, as well as couples who commissioned pair portraits to commemorate marriage. The paper suggests a methodology to be used for this type of research and also uses some specific characteristics of portraits to contribute to recent discussions in the field of numeracy studies, particularly with respect to gender differences in numeracy.