Do very high tax rates induce bunching? Implications for the design of income contingent loan schemes

Under the Higher Education Contribution Scheme graduates face a sharp discontinuity in their taxable incomes. At the first repayment threshold, they are required to pay a percentage of their entire income to reduce their debts. This results in an extremely high effective marginal tax rate. Using a sample of taxpayer returns we investigate whether taxpayers bunch below the repayment threshold. We find a statistically significant degree of bunching below the threshold, but the effect is economically small. The result has important implications for the design of income contingent university loan schemes.