Average buying price usually means total recorded purchase cost divided by the number of shares covered by that cost. The calculation weights each purchase by its quantity. Averaging the displayed prices alone gives the wrong answer when the quantities differ.
This article uses fictional Indian share purchases in rupees. It explains portfolio arithmetic without recommending another purchase or describing a tax calculation.
Start with the rupees spent
Suppose the first purchase is 10 shares at ₹100 each. That purchase costs ₹1,000 before charges. The second purchase is 30 shares at ₹120 each, costing ₹3,600 before charges.
Together, the purchases contain 40 shares and cost ₹4,600. Dividing ₹4,600 by 40 gives an average buying price of ₹115.
Taking the simple average of ₹100 and ₹120 would give ₹110. That calculation treats the two purchases as if their quantities were equal. In the actual example, three quarters of the shares were bought at ₹120, so the weighted answer sits closer to that price.
The same method works with more than two purchases. Each quantity is multiplied by its own price. The resulting amounts are added before the combined cost is divided by the combined quantity.
A contract note average has a particular scope
An order can execute through several trades at different prices. A weighted average on a contract note can summarise those executions. NSE's contract note guidance describes the use of a common weighted average alongside underlying trade details.
That average concerns the trades represented by the note. A portfolio's average buying price can span many notes and dates. The two averages can differ without either being incorrect because they cover different sets of transactions.
The source records also identify quantity and price separately from charges. A total amount debited from a broker account can include items beyond the shares' purchase value. Treating that whole debit as the price of a single share would mix incompatible units.
State how charges are handled
Return to the fictional 40-share holding. If a separate tracking method includes ₹40 of purchase charges in its cost figure, the total becomes ₹4,640. Dividing by 40 produces ₹116 per share instead of ₹115.
Both answers describe their stated arithmetic. They cannot be compared fairly until the treatment of charges is known. A price-only average and a cost-inclusive average are different measures.
Tax rules can apply different treatment to charges and acquisition records. A dashboard average does not establish a tax parcel's cost. The original trade details remain necessary even when a tracker displays a single rounded number.
What a sale changes in an average-cost tracker
In a simple average-cost tracker, selling 10 of those 40 shares leaves 30 shares with the same per-share average. Using ₹115, the remaining tracking cost is ₹3,450. Sale proceeds belong in a separate transaction and do not become a new purchase price.
That illustration describes average-cost bookkeeping only. It does not choose which parcel was sold for tax purposes. A broker's tax report can use a different method and therefore show a different cost attached to the sale.
Premature rounding creates another small discrepancy. Keeping the unrounded average during arithmetic and rounding only the displayed figure avoids multiplying a rounded price across a large quantity.
FinTarget's trades guide describes how logged buys update share counts and a weighted average cost. A later price decline changes the holding's market value, not the historical purchase amount. The average calculation records what happened. It does not say whether buying more at any price is appropriate.