One number from several purchases
Buying the same stock at different times means different prices — this weighs each purchase by its size, so a bigger buy at a lower price pulls the average down more than a small one. For a forward-looking comparison of lump sum versus spreading purchases out, see Lump Sum vs SIP.
Frequently asked questions
What is average cost / cost basis?
The weighted-average price you paid across all your purchases of a stock — total money spent divided by total shares bought. It's what you compare the current price against to see your real gain or loss.
Why does average cost matter?
If you bought at different prices over time, your break-even point isn't any single purchase price — it's the weighted average. This also matters for tax cost-basis reporting in many places.
Can I add more than 5 purchases?
Combine smaller batches into one row first (add up shares and total cost), or repeat the calculation in stages if you have many separate purchases.
Last updated: June 2026