Averaging Down Calculator

1. Enter how many shares you hold now in Current shares. It must be greater than 0.
2. Enter your average cost per share so far in Current average price. 0 is allowed.
3. Enter the price of one share in this new buy in New purchase price, not the total order value.
4. Choose how to enter the extra buy: Use additional investment or Use additional shares.
5. Enter the money you are putting in as Additional investment, or the share count as Additional shares.
6. Select Calculate to see the new average price, total shares, total cost and how far the average moved.
7. Select Reset example to go back to the values shown when the page opened.

The value you do not choose is never used. If you pick Use additional investment, whatever is left in the additional shares field is not passed to the calculation at all, so a stale figure cannot quietly change your result.

The values shown when the page opens are a hypothetical example chosen to show how the calculation works. They are not a real quote and no company or product is being recommended. This calculator holds no price, fee or tax figures of its own.

Averaging down means buying more of something you already own at a different price and then working out the weighted average cost of everything you now hold. It is not a strategy this page recommends; it is simply the arithmetic of putting two purchases together.

The word “down” describes the usual reason people do it, not a guaranteed outcome. A new purchase price lower than your current average price can bring the average down. A new purchase price higher than your current average price pushes the average up instead, which is sometimes called averaging up. This calculator does the same sum either way and labels the result Lower, Higher or No change in words, not by colour alone.

A lower average cost does not mean a smaller loss. Your total money at risk goes up every time you buy more, and the market price is unaffected by what you paid.

These are the formulas this calculator uses. Following them in order lets you check the result by hand.

New average price = ( current shares × current average price + additional shares × new purchase price ) ÷ ( current shares + additional shares )

• Existing cost = current shares × current average price
• Additional shares = additional investment ÷ new purchase price (in amount mode)
• Additional investment = additional shares × new purchase price (in share mode)
• Total shares = current shares + additional shares
• Total cost = existing cost + additional investment
• New average price = total cost ÷ total shares
• Average price change = current average price − new average price
• Average price change rate = change ÷ current average price × 100

The two input modes are the same equation read from either end, which is why the answer is identical whichever one you choose. Intermediate values are never rounded; only the numbers on screen are tidied up, so multiplying the figures you see by hand can differ slightly in the last digit.

If your current average price is 0 there is nothing to measure a percentage against, so the change rate is left uncalculated rather than forced to 0% or infinity. The change in money is still shown.

These are the same values the calculator shows when the page opens. They are a hypothetical example, not a real quote.

1. You hold 10 shares at an average price of 50, so your existing cost is 10 × 50 = 500.
2. You put in an additional investment of 800 at a new purchase price of 40.
3. Additional shares = 800 ÷ 40 = 20 shares
4. Total shares = 10 + 20 = 30 shares
5. Total cost = 500 + 800 = 1,300
6. New average price = 1,300 ÷ 30 = 43.33 (43.3333… before rounding)
7. The average moved from 50 to 43.33, about 6.67 lower, or roughly 13.33%.

Switching to Use additional shares and entering 20 against the same price of 40 gives exactly the same result, because 20 × 40 is the same 800. If you changed the new purchase price to 60 instead, the average would move upto about 55.71 — the same formula, a different direction.

• Current shares must be greater than 0. With no existing holding there is nothing to average against, so the calculator refuses the input instead of inventing an answer.
• A current average price of 0 is allowed. The new average price is still calculated; only the percentage change is left blank, because dividing by 0 has no meaning.
• An additional investment of 0 is allowed. Nothing is bought, so the totals stay exactly as they were.
• In amount mode the new purchase price cannot be 0 when the additional investment is above 0. There would be no way to work out how many shares the money bought.
• In share mode a price of 0 is accepted. The share count rises and the additional investment is 0, which is what a free allocation would look like.
• Fractional shares are accepted, both directly and as the result of dividing an amount by a price.
• Empty fields, letters, negative numbers and values above the limit shown under the table are not calculated, and the calculator tells you which field is wrong and why.

• This is a weighted average of what you paid, nothing more. It says nothing about what the shares are worth now.
• No live stock prices are fetched, and no market data is looked up anywhere on this page.
• Brokerage fees are not included. This engine has no field for user-entered fees, so none are applied.
• Taxes are not included, and no statutory tax rate is ever guessed or applied automatically.
• Exchange rates are not included. No currency conversion happens anywhere on this page.
• Because fees and taxes are excluded, the figure your broker shows can differ from the result here.
• A lower average price does not reduce a loss; it only restates what you paid on average.
• Buying more increases the money you have at risk in a single holding.
• Results are informational estimates based only on the values you enter.
• They do not guarantee any return and are not investment, legal or tax advice. No specific product is recommended.
• Intermediate values are not rounded; only the numbers on screen are rounded for display.
• Your inputs are calculated only in this browser and are never sent to or stored on a server.

This page and a general average price calculator use the same weighted average formula but answer slightly different questions.

• Averaging down (this page)starts from a position you already have — a share count and an average price — and adds one more purchase. That is the situation you are in when you are deciding whether to buy more.
• The Stock Average Price Calculator starts from a blank list and adds up every purchase you enter, one row at a time. That is the situation you are in when you are rebuilding a whole position from your trade history.

Both give the same answer for the same money and shares, because both are the same weighted average. Pick whichever matches the numbers you actually have in front of you.

If you want to rebuild a whole position from scratch rather than add one purchase to it, the Stock Average Price Calculator takes any number of buys, each with its own quantity and price, and gives the same weighted average.

To look forward instead of back, the Monthly Compound Interest Calculator grows a balance month by month with an optional monthly contribution, and the Compound Interest Calculator does the same over years. Both are hypothetical simulations and guarantee no return.

• Stock Average Price Calculator — add up every purchase you made
• Monthly Compound Interest Calculator — grow a balance month by month
• Compound Interest Calculator — project how a balance may grow