The single biggest lever in investment tax planning is often just time: holding an asset for more than one year before selling can move your gain from being taxed at your full ordinary income rate to a much lower long-term capital gains rate — sometimes the difference between 35% and 15% on the exact same dollar amount of profit.
Short-term capital gains (assets held one year or less) are taxed as ordinary income, stacked on top of your other income and taxed at your marginal rate. Long-term capital gains (held more than one year) get preferential rates — 0%, 15%, or 20% depending on your total taxable income — regardless of how high your ordinary income tax bracket is.
How Each Is Calculated
For short-term gains, the tax is calculated by adding the gain to your other taxable income and finding the additional tax generated by that increase — essentially, the gain is taxed at your marginal rate. For long-term gains, the applicable long-term rate (0%, 15%, or 20%) is determined by where your total income falls, and that rate is applied directly to the gain.
A Worked Example
On a $15,000 gain with $70,000 in other income (married filing jointly), holding short-term means the gain is taxed at your marginal rate, producing roughly $1,800-$3,300 in tax depending on exactly where the income lands across brackets. Holding the same investment long-term instead, the $15,000 gain likely falls entirely within the 15% long-term bracket, producing a flat $2,250 in tax — often lower, and always more predictable, than the short-term calculation.
Common Mistakes to Avoid
- Selling just before the one-year mark: waiting even a few extra days to cross the one-year threshold can move a gain from ordinary rates to the much lower long-term rate.
- Forgetting capital losses offset gains: losses realized in the same tax year (or carried forward) can offset gains and reduce your overall tax bill — this is called tax-loss harvesting.
- Not accounting for the Net Investment Income Tax: high earners may owe an additional 3.8% surtax on investment income above certain thresholds, on top of standard capital gains tax.
- Assuming all investment income qualifies for capital gains rates: dividends, interest, and short-term gains often don't get the same preferential treatment as long-term capital gains.
Bottom Line
The holding period alone can be worth thousands of dollars in tax. Use a Capital Gains Tax Calculator to compare your estimated tax under both short-term and long-term treatment before deciding when to sell.