Stock Average-down Calculator
Compute your <strong>new average share price</strong> after buying more, and find <strong>how many shares to buy to reach a target average</strong> (averaging down). It also shows valuation profit/loss and return rate. No market-data feed — it calculates only from your inputs, entirely in your browser.
※ A reference tool using only the values you enter; it is not linked to live prices and excludes actual fills, fees, taxes and FX. Not investment advice — investment decisions and outcomes are your own responsibility.
🔒 Inputs are calculated in your browser and never sent to a server.
What an average share price is
Your <strong>average price</strong> (cost basis per share) is the total amount paid divided by the total shares when you buy the same stock several times: (existing qty × existing avg + added qty × buy price) ÷ (existing qty + added qty). It is a <strong>quantity-weighted average</strong>, not a plain midpoint of two prices. Holding 100 shares at 10,000 and buying 100 more at 8,000 lands your average at the midpoint, 9,000. But adding only 10 shares moves it to about 9,818 — much closer to the original — because the new price carries less weight. The more shares you add, the harder your average is pulled toward the new price. Enter your current holding and the new purchase and this tool computes the weighted average before you commit.
Working out how many shares to average down
<strong>Averaging down</strong> means buying more after the price falls to lower your average. To find how many shares reach a target average, invert the formula: n = existing qty × (existing avg − target) ÷ (target − current price). Say you hold 50 shares at 20,000, the price is now 10,000, and you want a 15,000 average: n = 50 × (20,000 − 15,000) ÷ (15,000 − 10,000) = 50 shares. The math only works when <strong>current price < target < existing average</strong>. Set the target below the current price and the denominator turns negative — no amount of buying gets there. The closer the target sits to your existing average, the fewer shares you need. The tool checks these conditions and tells you whether a target is reachable.
Reading valuation P/L and return
Once the new average is set, you can read today's position instantly. <strong>Valuation P/L</strong> = (current price − average) × total shares, and <strong>return</strong> = (current price − average) ÷ average × 100%. With 200 shares at a 9,000 average and a current price of 8,000, that is (8,000 − 9,000) × 200 = −200,000, a return of about −11.1%. Watch a subtle trap: averaging down improves the <strong>percentage return</strong>, but because your invested capital grows, the absolute <strong>loss amount</strong> can get larger, not smaller. If the price never recovers, more money is simply tied up. Read the percentage and the won amount <strong>together</strong>; the tool shows both side by side so you can compare before and after.
Before you average down
A lower average does not erase a loss. <strong>Averaging down adds money to a falling stock</strong>, so if the business is deteriorating it can deepen the damage; if the company is sound and merely dipped, a lower average helps on the rebound. That judgment belongs to your analysis, not to a calculator. Note that these results exclude <strong>trading commissions, transaction tax, capital-gains tax and FX</strong>, so they differ from actual filled and settled amounts. The tool is not a live quote feed — it computes only from the values you type, so read the current price from your broker app and enter it yourself. Concentrating cash in one name also breaks diversification and raises risk, so decide your limit and position size first.
Frequently asked questions
Isn't the average just the midpoint of two prices?
No. It is a <strong>quantity-weighted</strong> average. Buying 100 shares at 10,000 and 10 shares at 8,000 gives about 9,818, not the 9,000 midpoint. The larger each purchase, the more it pulls the average toward its price.
Does averaging down reduce my loss?
Your <strong>percentage return</strong> can look better, but because your invested capital rises, the absolute <strong>loss amount</strong> may actually grow. It doesn't remove the loss — it lowers the rebound needed to break even. Read both figures together.
Does it pull in live stock prices?
No. This tool uses no market-data API and calculates only from the <strong>values you enter</strong>. Check your current price, holdings and average in your broker app and type them in.
Are fees and taxes included?
No. Results are a price-and-quantity <strong>estimate for reference only</strong>. Real trades add commissions and transaction tax, so filled and settled amounts will differ.