Cost Basis
Cost basis is what you originally paid for an investment, including fees and reinvested dividends. It's the number the IRS subtracts from your sale price to calculate your taxable capital gain (or loss) — so tracking it accurately can save real money at tax time.
Basis is what you paid plus reinvested dividends and commissions, and getting it wrong means paying tax twice on the same money — reinvested dividends were already taxed in the year received, so omitting them from basis taxes them again on sale. Which shares you sell also matters: the default is usually first-in-first-out, but specifying particular lots lets you realise the highest-basis shares first and shrink the gain. Brokerages report basis for most holdings bought recently, though transfers between firms and older positions can arrive incomplete. Inherited investments receive a step-up to their value at the date of death, which can erase decades of unrealised gains entirely — one of the most valuable provisions in the tax code.
Put it to work
ROI Calculator
Measure the return on any investment: total gain, total return (ROI), and the annualized return (CAGR) that lets you compare deals held for different lengths of time.
Capital Gains Tax Calculator
Estimate the tax on an investment sale and what you keep — and compare the long-term rate against the far higher one that applies if you sell too soon.