How to calculate your average purchase price
2026-11-07
How to work out a quantity-weighted average price and the return against today’s price, and why this is a calculation rather than investment advice.
Why you need an average price
When you buy the same item several times at different prices, the first and later prices differ. To judge whether today’s price is high or low, and whether your position is up or down overall, you need to know what you paid on average. The average purchase price is that reference point.
Weighted by quantity
Adding up the prices and dividing by the count is wrong, because a large purchase should count for more. Multiply each purchase’s quantity by its price to get the total cost, then divide by the total quantity.
- Total cost = the sum of (quantity × price)
- Average price = total cost ÷ total quantity
Suppose you buy 10 items at 10,000 won and then 5 more at 12,000 won. The total cost is 160,000 won for 15 items, so the average is about 10,667 won. A simple average of 11,000 won would be misleading.
Working out the return
Once you have the average, compare it with today’s price. Return = (current price − average price) ÷ average price × 100. If the current price is 11,000 won, the return is about 3.1 percent. A price below the average gives a negative figure.
What the calculation leaves out
The return here uses only your purchase prices and the current price. Fees, taxes, dividends and currency changes are not included. To know your real profit or loss, you need to add those costs yourself.
Keeping a clean purchase record
- Write the date, quantity and price for every purchase.
- Fractional quantities are accepted, so include partial purchases too.
- Add one row per purchase. If you enter a row by mistake, delete it and the average updates automatically.
An important note
This calculator only computes an average price and a return. It does not tell you when to buy or sell, and it is not investment advice or a recommendation. You are responsible for your own investment decisions and their results. Check the information carefully before you decide, and speak to a professional if you need to.