Average down calculator
Buying more of a stock that’s fallen? Your new average cost is the total spent across both buys divided by your total shares — and that average is exactly the price you need to break even.
How averaging down works
Averaging down means buying more of a stock at a lower price so your average cost per share falls. Because your two buys carry different prices, your new average is the total money spent divided by the total shares you now own:
new avg = (shares₁ × price₁ + shares₂ × price₂) ÷ (shares₁ + shares₂)
That new average is your breakeven price: sell there and you’re flat. To solve the reverse — how many shares you’d need to buy at a given price to reach a target average — rearrange the same equation:
shares to buy = shares₁ × (old avg − target) ÷ (target − buy price)
This is forward-looking trader math — it helps you plan a purchase and see your new breakeven. It’s a different job from a cost-basis calculation, which is tax-lot accounting used when you sell (FIFO, LIFO or average cost decide which shares are sold and what gain you report). Averaging down lowers your breakeven but also raises your total money at risk in one name — it doesn’t fix a broken thesis.
Illustrative math on the numbers you enter, not a recommendation to buy. Educational tool, not financial advice. Your figures never leave the page — the calculation runs entirely in your browser. The page loads standard pageview analytics, which never sees your numbers.
This math stops at what you typed in.
Tradune runs it continuously on your real holdings — with your money-weighted return next to a buy-and-hold SPY twin, and SEC insider filings flagged on the stocks you own.
Educational analytics — not investment advice.