Average Down Calculator
Enter the shares you own and the shares you plan to buy, and your new average cost per share appears instantly. You can also work backward to see how many shares to buy to reach a target average cost.
| Round | Shares | Price | Cost | Weight |
|---|---|---|---|---|
| Total | - | - | - | 100% |
Value at the current price
A lower average cost does not erase a loss you already have. If you put in more money and the price keeps falling, your dollar loss can end up bigger than before.
The share count is a theoretical value. Real fills happen at slightly different prices, and fees can change the result a little.
How to use
How this average down calculator works
This average down calculator shows your new average cost per share after you buy more of a stock, ETF or other asset you already own. Enter the number of shares you hold and the price you paid on average, then add up to five more purchases with their quantities and prices. The calculator returns your new average cost, your total shares, the total amount invested and how much your average cost changed in dollars and percent. If you also enter the current price, it adds the market value, profit or loss and return so you can see where you stand today. A second tab works backward: give it a target average cost and the price you can buy at, and it tells you how many shares you would need.
The formula
Your average cost per share is a weighted average. Add up everything you paid, then divide by the total number of shares:
average cost = (shares owned × average cost + Σ shares bought × price paid) ÷ total shares
Say you own 100 shares at an average of $100, then buy 50 more at $80. You have invested $10,000 + $4,000 = $14,000 in 150 shares, so your new average cost is $14,000 ÷ 150 = $93.33, which is 6.67% lower than before. Add a current price of $95 and your holdings are worth $14,250, a gain of $250 or about 1.79%. Without the extra purchase you would have been sitting on a $500 loss at $95, so the lower average cost moved your break-even point from $100 down to $93.33.
Working backward to a target
The second tab solves for the number of shares to buy. With q shares at an average cost of p, a target average cost of t and a purchase price of b, the shares to buy are:
shares to buy = q × (t − p) ÷ (b − t)
For example, you own 100 shares at $100 and want an average cost of $90 by buying at $80. The answer is 100 × (90 − 100) ÷ (80 − 90) = 100 shares. That costs $8,000, and afterwards you hold 200 shares with $18,000 invested, which is exactly $90 each. The formula only works when the purchase price is on the other side of the target from your current average: to lower your average cost you must buy below the target, and to raise it you must buy above it. If you enter a price that cannot reach the target, the calculator explains why.
What averaging down does and does not do
Averaging down lowers your cost per share, so the price does not have to recover as far for you to break even. It does not erase a loss that has already happened, and it increases the amount of money exposed to the same investment. If the price keeps falling, your dollar loss grows faster than before because you now own more shares. Many investors use a plan, such as buying more only if their original reason for owning the stock still holds, and they cap how much of their portfolio any single holding can become. This tool does the arithmetic, not the judgment, and nothing here is investment advice.
Dollar-cost averaging in one example
Dollar-cost averaging means investing a fixed dollar amount on a schedule instead of buying a fixed number of shares. Suppose you invest $300 a month for three months while the price is $10, $5 and $6. You buy 30, 60 and 50 shares, for 140 shares and $900 invested. Your average cost is $900 ÷ 140 = $6.43, lower than the simple average of the three prices ($7.00), because the same dollars buy more shares when the price is low. Enter the three purchases here as separate rounds to check it yourself.
Taxes, fees and your broker’s numbers
- Cost basis for taxes. In a taxable account your broker tracks the cost of each purchase (a tax lot). Unless you choose a different method, sales of stock generally use the first shares you bought first (FIFO), so your reported gain may not match a simple average. Mutual fund shares can often use an average-cost method.
- Wash-sale rule. If you sell at a loss and buy the same or a substantially identical security within 30 days before or after the sale, the loss is generally disallowed for that tax year. Check the IRS guidance or a tax professional.
- Fees and spreads. Many brokers charge no commission on stock trades, but you may still pay a bid-ask spread, and some assets carry fees. Add them to your purchase price if you want a more precise average.
- Fractional shares. The calculator accepts up to four decimal places, so it works with brokers that sell fractional shares.
Questions to ask before you buy more
- Has the reason I bought changed? A lower price is only a bargain if the underlying business or fund is still sound.
- How big will this position become? Use the total invested figure to check what share of your portfolio it represents after the purchase.
- Could I handle a further drop? Run the calculator with a lower current price to see the loss if the price falls another 10% or 20%.
- Is there a cheaper way to diversify? A broad index fund spreads the risk that a single company carries.
Frequently asked questions
What is average cost per share?
It is the total amount you have paid for an investment divided by the number of shares you own. If you bought 10 shares at $50 and 10 at $70, you paid $1,200 for 20 shares, so your average cost is $60 per share.
How do I calculate my new average cost after buying more?
Add the cost of the new purchase (shares times price) to the cost of your existing holding, then divide by the combined share count. This calculator does that for up to five additional purchases and shows each round in a table with its share of the total.
Does averaging down reduce my loss?
It lowers your break-even price, but it does not remove the loss you already have, and it puts more money into the same position. If the price keeps dropping, your total loss in dollars can become larger than it would have been without the extra purchase.
What does the target average cost tab do?
It tells you how many shares you would need to buy at a given price to reach a target average cost. It also shows the extra money required and your new totals. If the share count is not a whole number, the calculator suggests rounding up when your broker only sells whole shares.
Does the calculator include fees and taxes?
No. It uses the prices you type in. If you pay commissions or spreads, add them to your purchase price. Taxes depend on your account type, holding period and cost-basis method, so check with your broker or a tax professional.
Will my broker show the same average cost?
Often yes for a simple weighted average, but brokers may display tax-lot cost basis instead, and some adjust for dividends reinvested, splits or wash sales. Compare against your broker’s statement before relying on a figure for tax filing.
Is my information saved?
No. All calculations run in your browser and nothing you enter is uploaded or stored.