Dividend Basics

What Is Cost Basis? A Plain-English Guide for Dividend Investors

Your brokerage statement shows "cost basis" next to every holding, and it's the number that determines whether you're actually up or down on an investment — not just what the current price says.

The basic definition

Cost basis is what you actually paid for an investment, including the price per share and typically any fees or commissions. If you bought 10 shares at $50 each, your cost basis for that purchase is $500 (or $50 per share).

Unrealized Gain/Loss = Current Market Value − Cost Basis

If those same 10 shares are now worth $600 total, you have a $100 unrealized gain — "unrealized" because you haven't sold and locked it in yet.

Why cost basis matters

Two things hinge on cost basis: understanding your real performance, and taxes.

Performance-wise, the current price alone doesn't tell you whether an investment has been good for you — you need to know what you paid. A stock trading at $100 could be a big win if your cost basis was $40, or a loss if it was $150.

For taxes, when you eventually sell, your cost basis is subtracted from the sale price to determine your taxable capital gain or loss. Getting this number wrong on a tax return can mean over- or under-reporting what you owe, which is why brokerages are required to track and report it to the IRS for most securities.

What changes your cost basis

Cost basis isn't always a single, simple number — a few things commonly adjust it over time:

Multiple purchases at different prices. If you buy the same stock several times at different prices, your overall cost basis is typically averaged across all the shares you hold (though the exact method can depend on your brokerage and account type).
Reinvested dividends (DRIP). If your dividends automatically buy more shares instead of being paid out as cash, each of those reinvestment purchases adds to your cost basis at the price paid that day — it's a real purchase, even though you didn't manually place the order.
Stock splits. A split adjusts your per-share cost basis proportionally, without changing your total cost basis.
Corporate actions like spin-offs or mergers can also require a cost basis adjustment, usually detailed by the brokerage or the company involved.

How to track it without doing the math yourself

For a portfolio with a handful of trades, tracking cost basis by hand is manageable. Once dividends are reinvesting automatically and you're holding positions across more than one brokerage, doing this math manually gets error-prone fast — which is exactly why most investors rely on their brokerage's own reporting, or a tool that pulls it directly from the source.

See your real cost basis and gains automatically

Ledger Dividends connects to your brokerage and shows cost basis and unrealized gain/loss next to your actual holdings.

Try Ledger Dividends

This article is for general educational purposes only and isn't financial, investment, or tax advice. Cost basis rules can vary by account type, brokerage, and jurisdiction. Consult a licensed tax professional or financial advisor about your own situation.