This study investigated developmental differences in the relationship of probability and cost estimates to worrying. Adults, younger children (M age = 8.67 years) and older children (M age = 11.06 years) rated the extent to which they worry about a list of negative social and physical outcomes and provided subjective probability and cost estimates for the same outcomes. Adults reported worrying more about social outcomes and rated them as less ‘bad’ (or costly) but more likely to occur than physical outcomes. Unlike adults, children in both age groups reported worrying more about physical outcomes. However, similar to adults, they also rated social outcomes as less ‘bad’ but more likely to occur than physical outcomes. Regression analyses showed that probability ratings were the best predictors of worry in adults, both probability and cost ratings equally predicted worry in older children, but only cost ratings predicted worry in younger children.