Low fertility and longer life lead to population ageing and slower or declining population growth. While slower demographic growth reduces the need for saving, the ageing population imposes old age dependency costs which are particularly heavy for the public sector. Is fertility too low? The National Transfer Accounts project (NTA) provides data to quantify dependency costs. Given current age profiles of taxes and benefits, for rich and upper middle income countries about three births per woman would maximize the fiscal support ratio. But inclusive age profiles of consumption and labor income are more relevant for living standards, and the corresponding support ratios are maximized by fertility just above two births per woman. Going a step further and taking reduced saving into account, 1.5 birth per woman for upper middle income countries, and 1.8 birth per woman in rich industrial nations, would maximize living standards. In open economies these results would be slightly different. Consideration of human capital would also change results somewhat.