Capital Gains Tax Basics for Investors

When you sell an investment for more than you paid, the profit is called a capital gain, and the IRS wants its share. How much you owe depends on how long you held the investment and your overall income. Understanding these basics helps you make smarter decisions about when to sell and how to structure your portfolio.

Short-Term vs. Long-Term: The One-Year Line

The IRS draws a hard line at one year. Hold an investment for one year or less before selling, and any gain is short-term. Hold it for more than one year, and it's long-term.

This matters because short-term and long-term gains are taxed completely differently.

Short-term capital gains are taxed as ordinary income. Whatever tax bracket your salary falls into, your short-term gains get added on top and taxed at the same rates. That could be anywhere from 10% to 37% depending on your total income.

Long-term capital gains get preferential rates: 0%, 15%, or 20%, depending on your taxable income. For most people, this is significantly lower than their ordinary income tax rate.

How Gains Are Calculated

Your gain is the sale price minus your cost basis. The cost basis is generally what you paid for the investment, plus certain costs like broker commissions.

If you bought 100 shares at $50 each ($5,000 total) and sold them at $75 each ($7,500 total), your gain is $2,500.

Things get complicated when you've bought the same investment multiple times at different prices. Most brokers default to FIFO (first in, first out), meaning the oldest shares are considered sold first. You can often choose specific lots to sell, which lets you control which cost basis applies.

The 0% Rate Opportunity

The 0% long-term capital gains bracket is one of the most underused tax benefits available. If your taxable income is low enough, you can sell appreciated investments and pay zero federal tax on the gains.

This is particularly valuable in years when income is temporarily low: early retirement, career transitions, sabbaticals, or years when you're living off savings rather than earning a salary.

Even if you don't need the money, you can sell and immediately rebuy the same investment. This "harvests" the gain at the 0% rate and resets your cost basis to the current price. Future gains start from the higher basis.

Net Investment Income Tax

High earners face an additional 3.8% tax on net investment income, including capital gains. This applies if your modified adjusted gross income exceeds $200,000 (single) or $250,000 (married filing jointly). These thresholds aren't indexed for inflation, so more taxpayers hit them each year.

For someone in the 20% long-term capital gains bracket who also owes NIIT, the effective rate on long-term gains is 23.8%.

Losses Offset Gains

Capital losses offset capital gains dollar for dollar. If you have $10,000 in gains and $4,000 in losses, you only pay tax on $6,000 of net gains.

Losses are applied in a specific order: short-term losses first offset short-term gains, long-term losses first offset long-term gains. Then any remaining losses offset the other type.

If your losses exceed your gains, you can deduct up to $3,000 of net capital losses against ordinary income each year. Excess losses carry forward to future years indefinitely.

What This Means for Your Investing

Holding period matters. If you're close to the one-year mark and don't have an urgent reason to sell, waiting a few more days can mean the difference between a 37% tax rate and a 15% rate.

Timing matters. Realizing gains in low-income years costs less in taxes. Realizing losses in high-income years provides more valuable deductions.

Location matters. Capital gains in taxable accounts are taxable. The same investments in retirement accounts (401k, IRA, Roth) don't trigger capital gains tax when you rebalance or sell.

Reporting Requirements

Your broker sends you Form 1099-B showing proceeds from sales. They may or may not report cost basis, depending on when you acquired the investment. You're responsible for reporting accurate cost basis on your tax return, even if the broker doesn't have it.

Keep records of your purchases: dates, prices, and any adjustments. Good record-keeping now saves headaches at tax time.

This article is for educational purposes only and does not constitute tax advice. Consult a qualified tax professional for advice specific to your situation.