A model of labour supply is used to calculate Australias marginal cost of public funds, which is the appropriate cut-off benefit/cost ratio for an additional public project. The labour supply model incorporates effective average and marginal tax rates faced by the representative household in each gross income decile. These rates are estimated from the ABS 1988-89 Household Expenditure Survey. A simulation analysis is performed to calculate the effect on labour supply of a 1 per cent increase in marginal tax rates. The estimated changes in tax revenues and deadweight loss in each decile are used to estimate the marginal cost of public funds.