Average Cost Calculator
Last updated: 2026-06-25
Average cost (average purchase price / cost basis) is the total invested amount divided by the total shares. It is a quantity-weighted average, not a simple average of prices.
The formula is: average cost = Σ(buy price × quantity) ÷ Σ(quantity). Enter all of your buys to get the combined average cost.
Enter your buys
Average purchase price (cost basis)
0 KRW
| Item | Value |
|---|---|
| Total shares | |
| Total invested | |
| Number of buys | |
| Average cost |
Average cost is based on the raw execution price. To include buy fees, enter the fee-inclusive price. Results are for reference only.
How to use
- Enter your buys — enter the buy price (per share) and quantity for each purchase, one per row.
- Add rows — if you have more buys, press "+ Add buy" to add another row.
- View results — press "Calculate average cost" to see the average purchase price, total shares and total invested in a table.
How to calculate stock average cost
Average cost is the average price per share you paid when buying the same stock across several purchases. The key point is that it is a quantity-weighted average, not a simple average of prices. If you bought more at a higher price, the average cost is pulled toward that price.
| Round | Buy price | Quantity | Amount |
|---|---|---|---|
| 1st | 70,000 KRW | 10 | 700,000 KRW |
| 2nd | 60,000 KRW | 10 | 600,000 KRW |
| 3rd (averaging down) | 50,000 KRW | 20 | 1,000,000 KRW |
| Total | Avg 57,500 KRW | 40 | 2,300,000 KRW |
In the example above, the average cost is total invested 2,300,000 KRW ÷ total shares 40 = 57,500 KRW. It differs from the simple price average (70,000+60,000+50,000)÷3 = 60,000 KRW because the most shares were bought at the lowest (3rd) price.
Buying more below your current price is commonly called "averaging down." The lower the added price and the larger the quantity, the more your average cost drops. To find your actual profit/loss when selling, use the Stock ROI Calculator which factors in fees and the 0.18% securities transaction tax.
Frequently asked questions (FAQ)
How is average cost (cost basis) calculated?
The average purchase price is the total invested amount divided by the total shares. Sum (buy price × quantity) for all buys to get the total invested amount, then divide by the sum of all quantities. It is a quantity-weighted average, not a simple average of prices.
How much does averaging down lower my cost basis?
Buying more shares below your current price (averaging down) lowers your average cost. The lower the added price and the larger the added quantity, the more the average cost drops. Enter your existing buys and the additional buy to see the combined average cost instantly.
Are trading fees included in average cost?
This calculator computes the average cost based on the raw execution price. To include broker buy fees, enter the effective purchase price including fees, or compute profit/loss in the Stock ROI Calculator which factors in fees and taxes.
Can I know my profit/loss from average cost alone?
With your average cost, current price (or sell price) and shares held, you can estimate unrealized P/L: P/L = (current price − average cost) × shares held. For exact realized P/L, use the Stock ROI Calculator that factors in sell fees and the 0.18% securities transaction tax.
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Last updated: 2026-06-25