How Can I Avoid Double Taxation on NSOs?

Non-Qualified Stock Options (NSOs) can lead to unexpected tax surprises—particularly double taxation if the cost basis isn’t properly reported. This common but avoidable mistake can cause you to pay tax twice on the same income. Fortunately, with a bit of diligence and planning, you can avoid overpaying the IRS.

What Causes Double Taxation on NSOs?

Double taxation typically happens when there’s a mismatch in reported income and cost basis during the sale of shares acquired through NSOs. Here’s how it unfolds:

• When you exercise NSOs, the spread between the exercise price and the fair market value (FMV) of the stock is reported as ordinary income on your W-2.
• When you later sell the shares, your brokerage issues a Form 1099-B, which reports your cost basis and proceeds from the sale.
• However, some brokerages only report the exercise price as the cost basis—ignoring the income already taxed and reported on your W-2.

This incomplete cost basis can make it appear as if you have a larger capital gain than you actually do—resulting in tax being paid again on income that’s already been taxed.

Steps to Avoid Double Taxation

1. Adjust Your Cost Basis

Your true cost basis should include:

• The exercise price
• Plus the amount reported as W-2 income

Example: If your exercise price is $10 and the FMV at exercise is $40, your W-2 income is $30 per share. Your correct cost basis is $40—not $10.

2. Cross-Check Tax Forms

Compare your Form W-2 and Form 1099-B to ensure that:

• The income reported from the NSO exercise is accurate
• The cost basis on Form 1099-B is properly adjusted

If the cost basis is incorrect on the 1099-B, you must manually correct it when filing your taxes.

3. Consult a Tax Professional

A CPA or tax advisor who understands equity compensation can:

• Help adjust your cost basis
• Avoid costly filing errors
• Ensure compliance with IRS reporting requirements

The Bottom Line

Double taxation on NSOs is a common but preventable issue. With accurate reporting and professional guidance, you can keep more of your hard-earned equity gains.