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The Complete Guide to Capital Gains Taxes

I have paid more in capital gains taxes than most people earn in a year. That is not a brag -- it is a confession. For years I sold positions without thinking about tax consequences, and it cost me tens of thousands of dollars in unnecessary taxes. Here is everything I have learned the hard way, so you do not have to repeat my mistakes.

Long-Term vs. Short-Term Capital Gains: The Most Expensive Mistake

The single biggest tax mistake individual investors make is selling winners before the one-year mark. Short-term capital gains are taxed at your ordinary income tax rate -- which can be as high as 37%. Long-term gains get preferential rates of 0%, 15%, or 20%. That difference can easily be 15-20 percentage points on the same gain.

Here is a concrete example: You buy $50,000 worth of stock and sell it for $75,000. Your gain is $25,000. If you are a single filer making $100,000 and you sell after 11 months, that $25,000 is taxed at 24% (your marginal ordinary income bracket), costing you $6,000 in federal tax. But if you wait one more month and sell at the 13-month mark, the same gain is taxed at 15%, costing you only $3,750. You just saved $2,250 by being patient for 30 days. Multiply that across a lifetime of investing and the difference is enormous.

The Net Investment Income Tax (NIIT): The Hidden 3.8%

Most people do not know about the NIIT until it shows up on their tax return. If your modified adjusted gross income exceeds $200,000 (single) or $250,000 (married filing jointly), you pay an additional 3.8% tax on your investment income. This includes capital gains, dividends, interest, rental income, and royalties.

The NIIT was introduced as part of the Affordable Care Act in 2013 and applies to the lesser of your net investment income or the amount by which your MAGI exceeds the threshold. The thresholds are not indexed for inflation, which means more people fall into it every year. For high earners, the maximum federal rate on long-term gains is effectively 23.8% (20% + 3.8%), not 20%.

Tax Loss Harvesting: Free Money Every December

Tax loss harvesting is the practice of selling losing investments to realize capital losses, which offset your capital gains. Here is how the math works: losses first offset gains of the same type (short-term losses cancel short-term gains, long-term losses cancel long-term gains). Then excess losses cross over to offset the other type. And if you still have net losses after all that, you can deduct up to $3,000 per year against ordinary income, with unlimited carryforward.

I harvest losses every December without exception. Even in a great year, there are always individual positions that are down. Selling them to lock in the loss, then buying a similar (but not identical) investment to maintain exposure, is one of the few genuinely free lunches in investing. Over a 30-year investing career, disciplined tax loss harvesting can add 0.5-1.0% to your annual after-tax returns.

The Wash Sale Rule: Do Not Trip This Wire

The wash sale rule is the IRS's defense against aggressive tax loss harvesting. If you sell a security at a loss and buy a “substantially identical” security within 30 days before or after the sale, the loss is disallowed. The disallowed loss gets added to the cost basis of the replacement shares, so you do not lose the deduction forever -- it is just deferred.

Key things to know: the 30-day window applies in both directions (30 days before AND 30 days after). It applies across ALL your accounts, including IRAs. And “substantially identical” means you cannot sell the Vanguard S&P 500 fund and immediately buy the identical Vanguard S&P 500 fund. But you could buy a similar Fidelity S&P 500 fund -- the IRS has not clarified whether different funds tracking the same index are “substantially identical,” and in practice most advisors treat them as acceptable substitutes.

How to Minimize Capital Gains Taxes

State Capital Gains Taxes: The Second Bite

Federal taxes are only part of the picture. Most states tax capital gains as ordinary income, which means your state marginal rate applies on top of the federal rate. California's top rate of 13.3% means a high-income Californian can pay 37.1% all-in on long-term capital gains (20% + 3.8% NIIT + 13.3% state). Meanwhile, Florida, Texas, Nevada, Washington, Wyoming, South Dakota, Alaska, Tennessee, and New Hampshire have no state income tax on investment gains.

This is why so many tech founders, hedge fund managers, and retirees relocate to no-income-tax states before a major liquidity event. The tax savings on a single large sale can pay for the move many times over. I live in Miami Beach partly for this reason -- Florida has no state income tax, which saves me thousands every year on my trading gains.

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