The wage–fund doctrine is a concept from early economic theory that seeks to show that the amount of money a worker earns in wages, paid to them from a fixed amount of funds available to employers each year (capital), is determined by the relationship of wages and capital to any changes in population. In the words of J. R. McCulloch,

wages depend at any particular moment on the magnitude of the Fund or Capital appropriated to the payment of wages compared with the number of laborers... Laborers are everywhere the divisor, capital the dividend.

The economists who first stated this relationship assumed that the amount of capital available in a given year to pay wages was an unchanging amount. So they thought that as the population changed so too would the wages of workers. If the population increased, but the amount of money available to pay as wages stayed the same, the results might be all workers would make less, or if one worker made more, another would have to make less to make up for it and workers would struggle to earn enough money to provide for basic living requirements.

Later economists determined that the relationship of capital and wages was more complex than originally thought. This is because capital in a given year is not necessarily a fixed amount, and the wage–fund doctrine was eventually abandoned in favor of later models.