Cost Basis, Explained Simply
What you originally paid for an investment, used to figure your taxable gain.
Cost basis is the original amount you paid for an investment, and it is the number the tax on your profit is measured from.
Think of it as your starting line. When you eventually sell, the government compares your sale price to your cost basis to figure out your gain or loss. Your basis usually includes the price you paid plus any fees or commissions. If you reinvested dividends along the way, those add to your basis too, which is a detail a lot of people miss.
Why it matters is that a wrong or forgotten cost basis can cost you real money at tax time. If you underestimate what you paid, you make your gain look bigger than it was and hand the IRS more than you owe. Good records keep that from happening.
Here is a real-dollar example. You buy 100 shares at $20 each, so $2,000, plus a $10 fee. Your cost basis is $2,010. A few years later you sell for $3,000. Your taxable gain is $990, not the full $3,000, and not even $1,000, because that $10 fee counts. Small detail, but it lowers your bill.
When you own the same fund bought at different prices over time, your brokerage tracks an average or lot-by-lot basis for you. It is smart to keep your own statements too, especially if you ever switch brokerages.
Bottom line: Cost basis is what you paid, fees and reinvested dividends included, and keeping it accurate keeps your tax bill honest.
This is general education, not personal advice, so check with a licensed professional about your situation.
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