As the tax rate is no higher for higher incomes, it does not affect the family’s disposable income whether one partner earns all income alone or whether both partners do. In joint tax systems like Germany’s, or family-based regimes, such as France’s quotient familial, partners’ eamings are pooled and assessed at the same marginal rate. As the tax rate is based on partners’ joint income, it is irrelevant how much each partner contributes.