How to calculate your average cost
Your blended average cost is the total money you have invested divided by the total number of shares or units you hold. It is a weighted average, not the simple average of your entry prices — a bigger lot pulls the average closer to its price.
Average cost = total invested ÷ total shares
Add a row for every buy, enter the price and quantity, and the calculator sums each lot's price × quantity for you. Optional fees are amortised into the average so the figure reflects your true cost per share.
Worked example
You buy 100 shares at $10, then add
300 shares at $6.
Total shares = 100 + 300 = 400. Total invested = $1,000 + $1,800 = $2,800.
Average cost = $2,800 / 400 = $7.00.
Averaging down vs averaging up
Averaging down means adding to a position at a lower price than your original entry, which drags your average cost down and lowers the price you need to break even. Averaging up means adding at a higher price, raising your average as you build into a winner. The math is the same weighted mean in both cases — only the direction of the new price relative to your average changes. Use it to see exactly where your break-even sits before you commit more capital.
Frequently asked questions
- How do you calculate average cost across multiple buys?
- Add up the money you spent on every lot (price × quantity for each), then divide by the total number of shares or units you hold. That weighted average is your blended average cost per share — not the simple average of the prices.
- What is the difference between averaging down and averaging up?
- Averaging down means buying more at a lower price than your original entry, which pulls your average cost down. Averaging up means buying more at a higher price, which raises your average. The math is identical either way — it is the same weighted mean.
- Does this calculator include broker fees?
- Yes. Open the "Fees & commissions" section and enter your total fees across all lots. They are amortised into the blended average cost so the figure reflects your true cost per share.
- How many lots can I add?
- As many as you need. Use "+ Add lot" to add another entry row and the × button to remove one. Half-typed or empty rows are ignored, so the average only counts complete lots.