This paper addresses a question which is fundamental to the perceived legitimacy of the distribution of resources today: to what extent does unfairness in how assets came to be acquired in the past affect incomes and wealth now? To answer that question requires two things: first, a principle to determine what is, and what is not, a just acquisition of wealth or a just source of income; second, a means of using that principle to estimate what fraction of wealth and income is now unjust. I use a principle put forward by Robert Nozick to provide the first of these things and then use a model of wealth accumulation and economic growth to illustrate its implications for the scale of unfairness today. The greater is depreciation of assets, the higher are saving rates out of labour income and the less important is human capital the more transient are the effects of past economic injustices. I use data on the perceived unfairness of economic outcomes to see if there is any evidence that those features which the model implies should influence the durability of injustice help explain cross-country differences in attitudes towards unfairness.