Cost Basis Calculator

Track your investment cost basis across multiple purchases.

Total Cost Basis = (Shares1 x Price1) + (Shares2 x Price2) + ... + Fees\nAverage Cost Per Share = Total Cost / Total Shares
Example:\n100 shares @ $50 = $5,000\n50 shares @ $60 = $3,000\nFees = $10\n\nTotal Cost = $8,010\nTotal Shares = 150\nAvg Cost = $53.40/share

What is cost basis?

The original value of an investment for tax purposes, including purchase price plus any fees or commissions.

Why is cost basis important?

It determines your capital gains or losses when you sell. Accurate cost basis helps with tax reporting and investment decisions.

How do I calculate average cost basis?

Total cost (all purchases + fees) divided by total shares owned. This is your breakeven price per share.

Should I include trading fees?

Yes. All transaction costs increase your cost basis and reduce taxable gains (or increase losses) when you sell.

What if I have more than 3 purchases?

Calculate groups separately or use spreadsheet software for many transactions. The principle remains: total cost / total shares.

Does cost basis change with stock splits?

Yes. After a split, your cost basis per share is divided by the split ratio, but total cost basis stays the same.

How do dividends affect cost basis?

Cash dividends do not affect cost basis. Reinvested dividends (DRIP) create new purchases with their own cost basis.

What is adjusted cost basis?

Cost basis adjusted for corporate actions like stock splits, spinoffs, or return of capital distributions.