Average Cost (DCA) Calculator

What the average cost calculator does

When you buy the same stock more than once at different prices, your true cost is not the latest price or a simple average of the prices you paid — it is the share-weighted average. This tool adds up every dollar you invested and divides by every share you own, giving the single number that actually determines your breakeven and your profit or loss.

Dollar-cost averaging (DCA)

Dollar-cost averaging means investing a fixed amount on a regular schedule no matter what the price is doing. Because a fixed sum buys more shares when the price is low and fewer when it is high, your average cost naturally lands below the average price over a choppy period. DCA removes the stress of trying to time the market and turns investing into a simple, repeatable habit.

Averaging down — and its risks

Averaging down is buying more after a drop to pull your average cost lower, so a smaller bounce gets you back to breakeven. It is powerful when a quality asset is temporarily cheap — but dangerous when a stock is falling for real reasons, because you are committing more money to a loser. Use the calculator to see exactly where your new breakeven lands, then decide with clear eyes.

A quick example

You buy 10 shares at 100 (1,000) and later 10 more at 80 (800). You now own 20 shares for 1,800, so your average cost is 1,800 ÷ 20 = 90. The stock only needs to climb back to 90 — not 100 — for you to break even. Enter today's price and the tool shows your live profit or loss against that 90 basis.

Final word

A lower average cost is helpful, but it is only one input in a sound decision. Position size, why the price fell, and your overall plan matter more than the number alone. This calculator handles the arithmetic so you can focus on the judgement.

How average cost is calculated

Your average cost per share is a weighted average: total dollars invested ÷ total shares owned. Buying more shares at a lower price pulls the average down more than the same number of shares at a slightly lower price — the weights are the share counts, not the number of purchases.

Worked example: averaging down in three buys

Your breakeven drops from $50 to $42 — the stock now only needs to recover 40% of its fall (from $30 back to $42) for you to be whole, instead of 67% (back to $50).

Averaging down: the honest trade-off

A lower breakeven feels good, but averaging down always does the same thing under the hood: it concentrates more of your money in your worst-performing position. That's rational when the business is sound and the market is mispricing it; it's how investors destroy portfolios when the price is falling for a real reason. Two guardrails help: decide a maximum position size before the first buy, and never average down to "fix" a thesis that has already broken.

Dollar-cost averaging vs lump sum investing

DCA — investing a fixed amount on a schedule regardless of price — automatically buys more shares when prices are low and fewer when they're high. Historically, though, investing a lump sum immediately has beaten spreading it out roughly two-thirds of the time, simply because markets rise more often than they fall (Vanguard's well-known studies put it at about 68% of rolling periods). DCA's real value is behavioral: it removes the timing decision, keeps you investing through scary markets, and matches how most people actually receive money — as a paycheck.

Cost basis and taxes when you sell

The average shown here is the average-cost method, which US brokers apply by default mainly to mutual funds. For individual stocks the IRS default is FIFO (first-in, first-out), though you can designate specific lots at the time of sale to control your taxable gain. Selling specific high-cost lots can shrink the gain you realize — see our capital gains tax calculator to estimate the tax either way.

Using this calculator with your broker statement

Your broker's "average cost" column can differ from your own math for three common reasons: reinvested dividends created small extra lots you forgot about, a stock split multiplied your share count and divided your per-share cost, and commissions or fees were capitalized into the basis. To reconcile, list every fill from your trade history — including DRIP purchases — and enter each as a separate row here. If the numbers still disagree, the split is the usual culprit: a 2-for-1 split turns 100 shares at $42 into 200 shares at $21, leaving your total cost unchanged.

Average cost and DCA are two different questions

People use "DCA calculator" to mean two things. The first is accounting: I already bought at several prices — what is my average and breakeven? That is this tool. The second is planning: if I invest $500 every month into an index fund, what will it be worth? That is a forward-looking simulation driven by an assumed return, which our compound interest calculator handles with its monthly-contribution input. Keeping the two separate prevents a subtle mistake — projecting a portfolio using your historical average price says nothing about what the market does next.

Sources: Vanguard — Lump-sum vs. cost averaging · IRS Topic 703 — Basis of Assets. Last updated: July 9, 2026.