Stock Average Down Calculator

A bigger buy closes a bigger share of the gap, never the whole thing

The new average after a buy is a weighted mean of the old average and the buy price, weighted by share count. The fraction of the gap that closes is exactly the new buy's share of the total position afterwards. Buy 75 shares on top of 300, the buy is one fifth of the position, and the gap closes by one fifth. Buy as many as you already hold and the gap closes by half. Buy three times the position and three quarters.

The starting position in every row is 300 shares at 50.00 per share; the new buy fills at 40.00 per share, with no fee. The new average is exactly 50 minus 10 times the share of the gap that closes. To halve the gap from 50 to 45 you must buy as many shares as you already hold, which costs 12,000.00 here. To close three quarters of the gap you must buy three times the position, which costs 36,000.00. The new average never reaches the buy price itself, no matter how big the buy is: a weighted mean of two numbers sits between them.

What averaging down changes, and what it does not

The same position under the same market price loses the same amount of money before and after the buy, at the moment the buy fills. Buying more shares does not recover anything; it converts cash into exposure. The break-even price falls, the share count grows, the percentage of deployed capital that is at risk falls, but the dollar distance between the position's value and the cash put in is the same.

The loss column is identical in every row: 3,000.00. The total cost column grows by the buy each time, the position value grows by the same buy times the market price, and the two cancel. The percentage of capital deployed that is currently at risk does fall, because the denominator is bigger, and that is the real reason a buy lowers the percentage damage. The break-even price moves down with the average, so the price the position needs to reach to recover has come closer; the recovery then happens on a larger share count, which is what produces the catch-up effect.

A commission on the buy adds a known amount to the average

A flat commission on the new buy is divided by the total share count after the buy, and the result is the amount it adds to the per-share average. The arithmetic is exact: a 4.95 commission on 500 total shares adds 0.0099 per share to the average, which displays as 0.01. The break-even price follows the average up by the same amount, and the unrealized loss at the same market price grows by the fee.

Every row in this table starts from the same 300 shares at 50.00 and a 200-share buy at 40.00, which without any fee gives an average of 46.00. A commission on the buy pushes the per-share number up by the fee divided by the total share count, and the loss at 40 grows by the fee itself, because the cost basis grew by exactly the fee. A commission on the sale, if any, would push the break-even price up by the exit commission divided by the same total share count, and is not in the table because the page does not know your broker's exit fee.

The total cost basis is unchanged; the per-share number is divided

A stock split replaces the shares you hold with a new number, at a new per-share price. The total amount of money you have at risk is the same number it was the day before the split. A 2 for 1 split doubles the share count and halves the per-share basis. A 3 for 1 tripling does the same with a factor of three. A 1 for 2 reverse split halves the share count and doubles the per-share basis.

The right-hand column is the same 5,000.00 in every row. A split does not add or remove money from the position. If the split produces a fractional share, the broker usually pays cash in lieu at the post-split price, and that cash is taken out of the share basis. The page does not model dividend reinvestments, return-of-capital distributions, or tax lots: the cost basis a broker reports for tax purposes can differ from the arithmetic the tool runs, and that difference is its own subject, not something this page is trying to settle.

What averaging down actually does to the position

Averaging down is buying more of a stock you already hold at a lower price than your current average. The new average is the total cost of all the shares divided by the total share count, with the commission on the new buy added to the cost. If the buy price is below the current average, the new average is below the old one; if it is above, the new average is above the old one. The size of the move is proportional to the size of the buy relative to the position you already hold, and is never larger than the gap between the old average and the buy price.

What the move does not do is recover the loss. The cash you put in buys shares at a lower price than your current average, which lowers the price the position needs to reach to break even, but it does not add to the position's value. At the same market price, the position is worth the same number of dollars after the buy as it was before, because the value is the share count times the market price and the cost is the cash you put in. What changes is the percentage of deployed capital that is at risk: the cash is now spread over more shares, and the loss looks smaller as a share of what you have committed.

The reverse question is also a calculation. If you know the target average you want to reach and the price you are willing to pay, the share count that brings the average to that target is a one-step solve. The buy has to be at a price below the target, and the target has to be below the current average, otherwise the question has no answer by buying. To close half of the gap you must buy as many shares as you already hold, regardless of which numbers the average and the buy price happen to be; the ratio is structural, not a coincidence of the example.

For more than one additional buy, the page can be run twice. The first run returns the new average; that average becomes the starting average for the second run, with the second buy as the new buy. The result is the same as adding every buy at once, because the new average is a weighted mean and weighted means compose: the overall total is the sum of all the numerators divided by the sum of all the denominators, in any order.

When the buy is above the current average

Buying more of a stock at a higher price than your current average raises the average, not lowers it. The same arithmetic applies in the other direction: the new average sits between the old average and the buy price, weighted by the share counts, with the fee added. The page accepts the input and shows the move as positive. Whether raising the average is the right thing to do is a question the page does not answer; it shows the arithmetic and stops there.

The break-even price moves up by the same amount, and the position's distance to recovery grows. The dollar loss at the same market price still does not change, because the new shares were bought at that market price and the position is still worth the same number of dollars. What changes is that more of the deployed capital is exposed to the same number of dollars of unrealized loss, which makes the percentage of capital at risk go up rather than down.

Stock splits and the cost basis

A stock split is a corporate action that multiplies the share count and divides the per-share basis by the same factor, leaving the total basis unchanged. A 2 for 1 forward split turns 100 shares at 50.00 into 200 shares at 25.00, and the total is 5,000.00 in both cases. A 1 for 2 reverse split does the same in the opposite direction, turning 100 shares at 50.00 into 50 shares at 100.00. Brokers apply the change on the effective date and the per-share price the position shows is the post-split price from that point on.

Where the per-share basis can drift from the simple division is when the split produces a fractional share. Most brokers pay cash in lieu at the post-split price, and that cash is taken out of the share basis. The page accepts the cash as an input and reduces the share basis by the amount entered. Special dividends, return-of-capital distributions, and spin-offs are different corporate actions with different arithmetic; the page handles the split and the cash in lieu, and stops there.

The cost basis the broker reports for tax purposes can differ from the arithmetic the page runs, because tax lots allow specific share identification, and because some jurisdictions treat a wash sale or a return of capital differently. The page is not a tax tool. The numbers it produces are the cost basis the position would have under the simple averaging arithmetic; what shows up on a tax form is whatever your broker's tax lot accounting says it is, and the two should be reconciled against the broker's statement, not against this page.

What this page does not assume

• It does not assume a broker's fee schedule. The fee on the new buy is an input you supply, not a number the page knows. Different brokers charge different amounts, and the page does not try to model the difference.
• It does not assume fractional shares are supported. The reverse tool shows both the exact share count and the next whole share, because most retail brokerages fill only whole shares. If your broker does support fractional shares, the exact figure is the one to use.
• It does not assume a currency. All figures are in the currency you enter; the page does not convert between USD, GBP or INR, and the rate of conversion is yours to bring.
• It does not include dividends, dividend reinvestments, return-of-capital distributions, or any other corporate action other than the split. Those change the cost basis in different ways and the page does not model them.
• It does not assume the new buy actually fills at the price you entered. A limit order, a market order at a different time, and a stop order can all produce a different fill price, and the page only knows the price you put in.

What this page does not calculate

• No tax lots or specific share identification. The cost basis the page produces is the averaging arithmetic. What your broker reports for tax purposes is set by your broker's tax lot accounting, including the rules for wash sales and specific share identification. The two can differ, and only the broker's statement is authoritative for tax.
• No portfolio-level cost basis. The page handles one position at a time. If you hold the same stock in two accounts, the cost basis of each account is calculated separately, and the combined position's cost basis is the sum of the two, not the average.
• No option cost basis. A call option or a put option has its own cost basis arithmetic, including the multiplier (one contract is 100 shares) and the expiry. The page can be used on the share equivalent (contracts times the multiplier), but the options position itself has different rules.
• No multiple buys in a single run. The page handles one existing position and one new buy. To add more than one buy, run the page again with the new buy as the next input; the weighted mean of all the buys is the same as adding them all at once, in any order.
• No broker commissions, exchange fees or SEC fees on the buy. The fee is a single number you supply. If your broker charges more than one fee on a buy, combine them before entering the total.

Related tools on this site

The lot size calculator answers the question that decides how big the position is in the first place. The new buy on this page is a position-sizing decision; the lot size calculator is where that decision is made before the buy is placed.

The drawdown calculator shows what a run of losses does to a percentage-sized position. Averaging down raises the exposure that a drawdown acts on, and the same fall costs more on a bigger position.

The risk reward calculator takes the other half of the picture: the ratio between what a trade can earn and what it can lose, and what win rate that ratio demands. A position with a lower average after averaging down has a smaller distance to break even, and that distance shows up as the reward side of the trade.

Frequently asked questions

What is a stock average down calculator?

It is a tool that takes the position you already hold, the buy you are considering, and (optionally) the commission on that buy, and returns the new average cost per share, the total cost, the break-even price, and what the position is worth at the current market price. This page does that, and also answers the reverse question, and recomputes the cost basis after a stock split.

How do you calculate the average down stock price?

Add the cost of the new buy to the cost of the position you already hold, and divide by the total share count. If the buy comes with a commission, add that to the numerator. The result is the new average cost per share. For 300 shares at 50.00 and a 200-share buy at 40.00 with no commission, the new average is (300 times 50 plus 200 times 40) divided by 500, which is 46.00.

What is the averaging down formula?

The new average is a weighted mean of the old average and the buy price, weighted by share count, with the fee added. The new average equals the old average minus the gap between the old average and the buy price, multiplied by the new buy's share of the total position afterwards. That is, new average equals A1 minus (A1 minus P) times S2 divided by (S1 plus S2). The fee adds a per-share amount of fee divided by total shares.

How many shares do I need to buy to lower my average to a target?

The number of shares to buy is the existing share count times the gap between the current average and the target, divided by the gap between the target and the buy price. If a 4.95 commission is on the buy, the commission is added to the numerator. The exact share count is rarely a whole number, and the page shows the next whole share as well. To close half the gap you must buy as many shares as you already hold, regardless of the prices.

Does averaging down reduce my loss?

At the same market price, the dollar loss is unchanged at the moment the buy fills. The cash becomes shares at the lower price, the position's value grows by the buy, and the cost grows by the same buy plus any fee. What does fall is the percentage of capital deployed that is at risk, because more capital is in the position. The break-even price also falls, and the recovery happens on a larger share count, which is the catch-up effect most people mean when they say averaging down works.

What is the difference between average cost and break-even price?

The average cost is what the position cost per share, including the fees on the buys. The break-even price is the market price at which selling the position returns the cash you put in. They are the same number when there is no commission on the sale; if the sale has a commission, the break-even price is higher than the average cost by the exit commission divided by the total share count. The page shows the average cost and notes the effect of an exit commission, without modelling the exit commission itself.

Does a stock split change my average cost?

It changes the per-share number, and leaves the total cost basis unchanged. A 2 for 1 split doubles the share count and halves the per-share basis; a 1 for 2 reverse split halves the share count and doubles it. The total amount of money you have at risk before the split is the same number it is after. If the split produces a fractional share and the broker pays cash in lieu, the cash is taken out of the share basis.

How do I calculate my cost basis after a stock split?

Multiply the share count by the split ratio to get the new share count. The total cost basis before the split, minus any cash in lieu of a fractional share, divided by the new share count, is the cost basis per share after the split. The page does the calculation for the inputs you enter. The result is the basis in the share lot; tax lot accounting, which can identify specific shares, is a different arithmetic that the page does not handle.

Is averaging down the same as dollar cost averaging?

No, and the difference is the trigger. Averaging down is a discretionary buy when the price has fallen below the price you paid. Dollar cost averaging is a fixed schedule of buys regardless of the price. The arithmetic of the new average is the same in both cases; what differs is why the buy is being made, and that is a question the page does not answer.

Does this work for shares in the UK or India?

The arithmetic is the same in any currency. The fee schedule is yours to bring; what a UK or Indian broker charges for a trade is not a number the page knows. The tax treatment of the cost basis is set by the rules in your jurisdiction, and the page does not try to model that. Enter your share count, your average cost in the currency you trade in, and the buy, and the result is the new average in the same currency.

Can I use it for options or for crypto?

For options, the page runs on the share equivalent (contracts times the contract multiplier, typically 100 for a standard US equity option). The page does not model the time decay, the strike, or the expiry. For crypto, the share count is the unit count and the price is the price per unit, with fractional units allowed. The fee is a single number on the buy. The arithmetic is the same; the inputs are the only difference.

What makes one average down calculator better than another?

Three things, in order of how often they are missing. Whether the commission on the buy is added to the cost basis, so the break-even price is correct. Whether the page also answers the reverse question, so you can work from a target average to the share count instead of the other way around. Whether the page handles a stock split without losing the cost basis. Most free pages skip the commission and skip the split, and they give you an average cost that is too low and a basis that is wrong after a corporate action.