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What are the tax implications of exercising options early?
The difference is whether your options qualify as incentive stock options (ISOs), or whether they are non-qualifying options. If your options meet all of the criteria for being ISOs (see here), then (a) you are not taxed when you exercise the options.  You treat the sale of the underlying stock as a long term capital gain, with the basis being the exercise price (S). There is something about the alternative minimum tax (AMT) as they pertain to these kinds of options.  Calculating your AMT basically means that your ISOs are treated as non-qualifying options.  So if your exercise bumps you into AMT territory, too bad, so sad. If you exercise earlier, you do get a clock ticking, as you put it, because one of the caveats of having your options qualify as ISOs is that you hold the underlying stock (a) at least two years after you were granted the options and (b) at least one year after you exercise the options.