Why it has to be a weighted average
If you bought a stock twice, your average cost is not the midpoint of the two prices. It is everything you spent divided by every share you hold, which is a different number whenever the two purchases were different sizes.
Buy 100 shares at $50 and 150 at $40 and the naive answer is $45. The real answer is $44.00: $5,000 plus $6,000 is $11,000, across 250 shares. The bigger purchase pulls the average toward its own price, and the gap widens as the purchases become more lopsided. Buy 100 at $50 and 900 at $40 and the average is $41, nowhere near the $45 midpoint.
This matters beyond tidiness. Your average cost is your break-even price and, in a taxable account, your cost basis for working out gains. Getting it from a rule of thumb rather than the arithmetic puts an error into both.
The recovery gap, and why losses hurt more than they look
Here is the part that surprises people. Your average is $40 and the stock trades at $32. You are down 20%. The gain you need to get back is not 20% — it is 25%.
Both figures are correct; they are measured against different things. The loss is $8 against your $40 average. The recovery is that same $8 against the $32 the stock is actually worth now, and $8 is a quarter of $32. Since any future rally starts from today's price, the recovery percentage is the one that describes what has to happen.
The asymmetry compounds as losses deepen:
- Down 10% — needs +11.1%
- Down 20% — needs +25%
- Down 33% — needs +50%
- Down 50% — needs +100%
- Down 75% — needs +300%
This is the honest argument for cutting a position early and the honest argument against averaging down into something that keeps falling. Enter a market price under More Options and the calculator shows both numbers side by side.
What to put in each field
Shares and price each. One row per purchase, with the price you actually paid rather than the price you meant to pay. Fractional shares are fine. The order of the rows makes no difference to the result — only the share counts and prices matter — so you can enter them in whatever order you have the records.
Shares you hold and your average cost. On the averaging-down tab, the position as it stands. If you do not know your average, work it out on the first tab and bring the answer across.
Amount to add. Money, not shares, because that is usually how the decision is framed — you have a certain amount to commit and want to know what it buys. The calculator converts it at the price you enter.
Target average. On the third tab, where you want the average to end up. It has to sit between the price you would pay and your current average, and the calculator says so plainly if it does not, rather than printing an impossible number.
Where fees fit, and why they raise your basis
Commissions are part of what the shares cost you, so they belong in the average. Buy 100 shares at $50 with a $10 commission and you spent $5,010, making your real cost $50.10 a share. US tax rules take the same view: purchase commissions are added to cost basis rather than deducted separately.
On a large position this is a rounding difference. On a small one it is not, and it is worth remembering before splitting a modest purchase across several orders — four $25 buys with a flat fee each can cost noticeably more per share than one $100 buy. Enter the total of your buy fees under More Options and the average adjusts.
Selling fees are a separate matter and are not included here, because they depend on an exit you have not made yet. If you want a true round-trip break-even, add your expected sell commission per share to the figure this page gives you.
The cost of chasing a target average
The third tab answers a specific question: how many shares at today's price would bring my average down to a chosen number? The formula is simple enough — your holding times the gap between your average and your target, divided by the gap between your target and the price you are paying — but its behaviour is what deserves attention.
Start with 100 shares averaging $50, with the stock now at $30:
- Target $45 — 33 shares, about $1,000
- Target $40 — 100 shares, about $3,000
- Target $35 — 300 shares, about $9,000
- Target $32 — 900 shares, about $27,000
- Target $30.50 — 3,900 shares, about $117,000
The requirement runs away as the target approaches the current price, because you are trying to drag the average almost all the way down to what you are paying, and only an enormous new position can outweigh the old one. The last dollar of average reduction costs far more than the first.
Read that as a constraint rather than a plan. If reaching your target needs several times your existing position, the honest conclusion is usually that the target is the wrong goal, not that you should commit the money.
When averaging down makes sense, and when it does not
Averaging down always lowers your average. That is arithmetic, not judgement, and it is why the strategy feels productive even when it is not.
The test of whether you would buy it fresh today usually comes down to what the price implies about future earnings. Our P/E ratio calculator puts a number on that.
The judgement is whether you would buy this stock today at this price with fresh money, knowing nothing about what you already own. If yes, adding is simply buying something you want at a better price. If the honest answer is that you are adding because you are down and want the average to look better, the position is making the decision rather than you.
Two practical constraints. First, concentration: three rounds of averaging down can leave a single holding at three or four times its intended size, and a position that has fallen every time you added is precisely the one you least want oversized. Second, the reason for the fall: averaging down assumes the drop was noise. If earnings deteriorated, the dilution was real or the sector thesis broke, the lower price is information rather than an opportunity.
What this calculator does not cover
- Tax lots. It computes an average across all purchases. Selling specific lots — FIFO, LIFO or specific identification — can produce a very different taxable gain from the same trades, and US brokers let you choose.
- Selling fees or spreads. Buy fees only, since the exit has not happened.
- Dividends and splits. Neither is modelled, and both change your effective basis per share.
- Currency effects. Buying a foreign-listed stock carries a second cost basis in the exchange rate that this page does not see.
- Whether to add. It shows what an addition would do. It has no view on whether the company is worth owning.
Frequently asked questions
How do I calculate my average price per share?
Divide everything you have spent by every share you own. Multiply each purchase's share count by its price, add those together, add any commissions, then divide by the total shares. Buying 100 shares at $50 and 150 at $40 means $11,000 across 250 shares, or $44.00 each. Averaging the two prices instead gives $45, which is wrong whenever the two purchases were different sizes.
Why is my break-even higher than I expected?
Because the gain needed is measured from where the stock trades now, not from your average. If your average is $40 and the stock sits at $32, you are down 20% against your average but you need a 25% rally to get back, since $32 has to climb $8 and $8 is a quarter of $32. The gap widens fast as losses deepen: a position down 50% needs a 100% gain to recover.
Do commissions and fees change my average cost?
Yes, and they raise it. A $10 commission on 100 shares bought at $50 makes the real cost $5,010, so the basis is $50.10 a share rather than $50. US tax rules treat purchase commissions as part of cost basis for exactly this reason. The effect is trivial on a large position and can be significant on a small one, which is worth remembering before splitting a modest buy across several orders.
Does averaging down always lower my break-even?
Buying below your current average always lowers the average, yes. Whether that helps is a separate question, because it also increases the amount of money exposed to the same position. Three rounds of averaging down can leave you with three or four times the original stake in a stock that has fallen every time you bought. The lower break-even is real; so is the larger loss if the decline continues.
How many shares do I need to buy to reach a target average?
The calculator solves it directly, but the shape of the answer matters more than the number. Shares needed equals your current holding times the gap between your average and your target, divided by the gap between your target and the price you are paying. As the target approaches the current price the denominator shrinks toward zero and the requirement runs away: with 100 shares averaging $50 and a price of $30, reaching $40 needs 100 more shares, while reaching $30.50 needs 3,900.
Can I average down on any asset?
The arithmetic works for anything priced per unit, so stocks, ETFs, funds and crypto all behave the same way here. What differs is whether the reasoning holds. Averaging down assumes the price fell for reasons that will reverse, which is a claim about the underlying asset rather than about the math. Applying it to something with no earnings, no assets and no cash flow is a bet that sentiment returns, and the calculator has no view on that.
These results are estimates for general information only and are not investment advice. Averaging down increases the amount of money exposed to a single position and can increase losses if the price continues to fall. Cost basis for tax purposes depends on your broker's lot-selection method and your jurisdiction's rules, which this page does not model. Confirm any figure against your own broker statements, and speak to a qualified financial adviser or tax professional before acting.