Mixed ISO and NSO Exercises: Complex Interactions and AMT Credits

Exercising both ISO and NSO options creates the most complex tax scenario because the two types interact: NSO income can push you toward or away from AMT, ISO preferences add AMT items, and basis tracking must be kept separate. Learn why optimizing one option type in isolation can increase total taxes.

AMT from ISOs may interact with NSO income. NSO exercises increase your regular tax income (since the spread is ordinary income), which can push you closer to or further from AMT territory. Meanwhile, ISO exercises add AMT preference items. The interplay means exercising both in the same year requires modeling both the regular tax and AMT systems simultaneously.

Track basis separately for each type. ISO shares have a different basis for regular tax and AMT purposes. NSO shares have the same basis for both systems (FMV at exercise). If you hold both types and sell in the same year, your CPA must track each lot separately to calculate gains correctly under both tax systems.

AMT credit carryforward may apply. If you paid AMT in a prior year due to ISO exercises, you may have an AMT credit (Form 8801) that can offset regular tax in future years. NSO exercises in the current year increase your regular tax, which may allow you to use more of that credit. This is a silver lining that many taxpayers miss.

The tradeoff: The interaction between ISO and NSO tax treatment means that optimizing one type in isolation can accidentally increase the tax on the other. A CPA must model both together to find the true minimum total tax.