📉 물타기 평단가 계산기

What this tool does

Enter your current average price and quantity plus the price and quantity you plan to add, and it instantly calculates the new average cost after averaging down (or up), total quantity, total invested, the percentage change in average cost, how many times your investment has grown and the added purchase's share of the total. Use it to see how far an extra buy pulls your average down when a stock or coin falls, or how much it raises the average when you add on the way up.

How it is calculated

Average cost is a weighted average: total invested ÷ total quantity. New average = (old average × old quantity + add price × add quantity) ÷ (old quantity + add quantity), shown to two decimals. Change = (new average − old average) ÷ old average × 100; investment multiple = new total ÷ old total; added share = add quantity ÷ new quantity × 100. With the defaults of 100 units at 10,000 plus 100 more at 5,000: (1,000,000 + 500,000) ÷ 200 = a new average of 7,500, a change of −25.00%, 1.5 million invested, 1.5× the original, and a 50% added share. A falling average shows the change in red, a rising one in green. Quantities accept decimals, so it works for assets bought in fractions such as coins. Amounts are labelled in won, but the maths works for any currency.

• Enter your current average price and quantity (the current total is calculated automatically)
• Enter the price and quantity of the extra buy (its total is calculated too)
• The new average, total quantity and total invested appear immediately
• Average change = (new average − old average) ÷ old average × 100
• Use the investment multiple and added share to judge how big this buy is

Things to know

• Average cost is weighted, not a simple mean. Buys at 10,000 and 5,000 only average 7,500 when the quantities match; a smaller add moves the average only a little.
• A lower average does not mean a smaller loss. The loss so far is unchanged and you have simply invested more; only the rise needed to break even is smaller.
• To work back from a target average: required quantity = old quantity × (old average − target) ÷ (target − add price). Enter the result to check.
• An added share above 50% means this buy outweighs what you already hold. Together with the multiple, it shows how concentrated you are becoming.
• Fees and taxes are excluded. Broker apps may show a slightly higher average because buy fees are included.
• For several buys, put the new average and quantity back into the current fields and enter the next buy.
• Amounts display in won, but because the formula is the same, dollar prices give correct ratios and averages too.

Frequently asked questions

Results are for information only and are not investment advice. Decisions and their consequences are your own.