2008 The Economic Society of Australia We develop a simulation model explaining the accrual of retirement wealth gained from working one year beyond retirement and from this calculate an implicit tax rate on the additional year's work. We find that the pre-July 2007 Australian tax on retirement benefits was biased in favour of ages 59 and less, while the implicit rate was positive on retirement past 59. We also use the results of a national survey of 2,500 households (ASRAM SURVEY) to determine the likely response to the tax changes implemented in July 2007 and find that half those sampled are either very likely or likely to change their expected retirement dates in response to the tax changes.