I undertake a quantitative investigation into the short run effects of changes in the timing of proportional income taxes for model economies in which heterogeneous households face a borrowing constraint. Temporary tax changes are found to have large real effects. In the benchmark model, a temporary tax increase reduces aggregate consumption on impact by around 29 cents for every additional dollar of tax revenue raised. Comparing the benchmark incomplete markets model to a complete markets economy, income tax cuts provide a larger boost to consumption and a smaller investment stimulus when asset markets are incomplete.