Cost basis is the total amount you've invested in acquiring an asset, serving as your reference point for calculating gains or losses. This includes the purchase price plus any fees, commissions, or other costs directly tied to the acquisition. When you eventually sell the investment, the difference between your sale price and cost basis determines your taxable capital gain or deductible loss.
How It Works
Your cost basis starts at purchase and may be adjusted over time. For example, if you buy shares at $10 per share plus $100 in brokerage fees for 100 shares, your cost basis is $1,100 total, or $11 per share. If you later receive a dividend that you reinvest, that amount gets added to your cost basis. When you sell those shares at $20 each, you'd calculate your gain as $2,000 (sale price) minus $1,100 (cost basis) for a $900 profit.
Why It Matters for Investors
Cost basis directly impacts your tax bill. Higher cost basis means lower taxable gains—and lower taxes. This is why angel investors need meticulous record-keeping from day one. The IRS requires you to report cost basis accurately, and errors can trigger audits or penalties. Additionally, understanding cost basis helps you make strategic decisions about which investments to sell first during portfolio rebalancing.
Different cost basis methods exist. The first-in-first-out (FIFO) method assumes you sell your oldest shares first, while specific identification lets you choose exactly which shares to sell, optimizing your tax outcome. Many investors benefit from consulting a tax professional to select the method that best serves their financial goals.
Example
You invest $50,000 in a startup's Series A round, including $1,000 in legal fees. Your cost basis is $51,000. Two years later, after the company's Series B round, your shares are valued at $120,000. You haven't realized any gains yet—they're unrealized. But if you sell $60,000 of those shares, you'll owe capital gains tax on the difference between $60,000 (proceeds) and your proportional cost basis of approximately $25,500, netting a taxable gain of roughly $34,500.
Key Takeaways
- Cost basis is your total investment amount and forms the baseline for calculating capital gains or losses
- Maintain detailed records of all purchases, fees, and adjustments to accurately track cost basis
- Your choice of cost basis method (FIFO, specific identification, etc.) significantly impacts your tax liability
- Understanding cost basis is essential for strategic tax planning and informed exit decisions