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Prior studies of call option early exercise either ignore personal taxes or simplify the impact of taxation. When making an early exercise decision, the option holder should compare the after-tax cash flows from exercise with the after-tax cash flows from selling the option. Due to the differential taxation of option and share transactions, it is possible for exercise to be wealth-maximizing after tax even when it would not be the rational decision on a before-tax basis. By incorporating personal taxes on the option, underlying share and dividend this paper shows that tax can potentially explain a large portion of early exercise events classified as 'irrational' in previous studies. Copyright (c) 2010 Blackwell Publishing Ltd.

Share and option transactions are taxed differently, which means that the after-tax cash flows used to establish put-call parity will differ depending on which option is exercised. This paper derives the after-tax put-call parity relationship for European and American options with or without dividends. Using Australian data for the period July 1999 to June 2002, the after-tax put-call parity relationship explains 88.3 per cent of no-tax lower boundary violations and 78.8 per cent of no-tax upper boundary violations. The violation are larger for more thinly traded securities, providing some evidence that traders are able to profit from the tax discontinuities that affect investors in options. Copyright (c) The Authors. Journal compilation (c) 2009 AFAANZ.

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