Stock Average Price Calculator

Weighted average cost is the total capital you have deployed in a stock divided by the total number of shares you hold. It gives each buy price a weight proportional to how much capital went in at that price.

Formula: average cost = Σ(price_i × qty_i) ÷ Σ(qty_i)

Example: you bought 10 shares at ₹500 and 20 shares at ₹450.

• Total invested: 10 × ₹500 + 20 × ₹450 = ₹14,000
• Total shares: 10 + 20 = 30
• Weighted average cost: ₹14,000 ÷ 30 = ₹466.67

The simple average (₹500 + ₹450) ÷ 2 = ₹475 is wrong — it ignores that you bought twice as many shares at the lower price. The weighted average correctly reflects that more capital was deployed at ₹450.

Your break-even price is your weighted average cost. If the stock is currently below ₹466.67, you have an unrealised loss. Your unrealised P&L = (current price − average cost) × total shares held.

Break-even price tells you when your unrealised P&L becomes zero. It does not measure your return. Two scenarios with identical average costs can have very different XIRR values:

• Scenario A: bought at ₹500, averaged down at ₹450, stock recovers to ₹467 (your average cost) in 3 months. Approximate XIRR: ~0% — you recovered capital but earned nothing.
• Scenario B: same buys, same average cost of ₹467, stock recovers to ₹467 in 2 years. XIRR: meaningfully negative in real terms (opportunity cost of 2 years at zero gain).

XIRR (Extended Internal Rate of Return) solves for the annualised return that makes the net present value of all your cash flows equal to zero:

Σ C_i / (1 + r)^{(d_i − d₀) / 365.25} = 0

where each buy is a negative cash flow and today's market value is a positive cash flow. XIRR accounts for the fact that ₹5,000 deployed 18 months ago has a different time-value than ₹9,000 deployed 6 months ago.

To activate XIRR in this calculator: enable "Add dates", enter a buy date for each tranche, and enable "Current price". The cashflow chart appears automatically once all inputs are complete.

Benchmark: Nifty 50 TRI has delivered approximately 13–15% XIRR over rolling 10-year periods. If your stock's XIRR is materially below this — especially after averaging down — the capital would have been better deployed in an index fund.

The average cost this calculator shows is for decision-making — understanding your break-even price and portfolio exposure. It is not the cost basis you use for your income tax return.

For capital gains in your ITR, use FIFO.

CBDT Rule 8AA under the Income Tax Rules 1962 (as amended) mandates that cost of acquisition of listed shares must be determined on a First-In, First-Out basis. When you sell shares, the oldest shares in your account are treated as sold first, and each lot's purchase price is used for that specific lot's capital gain computation.

Your broker's Tax P&L or Capital Gains Statement — available in the reports section of most Indian brokers — already applies FIFO correctly and produces the numbers for Schedule 112A. Use that statement for your ITR. Use this calculator for understanding your position.

Long-term capital gains on listed equity: gains above ₹1.25 lakh per year are taxed at 12.5% (Finance Act 2024, effective 23 July 2024). Short-term capital gains: 20%. Holding period for LTCG: 12 months for listed shares. Consult a qualified CA for your specific situation.

• Averaging down on a deteriorating business: A lower average cost does not make a bad business a good investment. If revenue is falling, margins are compressing, or promoter integrity is in question, the stock's fall may be informational — the market is pricing in a weaker future. More capital into that position amplifies the loss.
• Confusing break-even with return: Getting back to your average cost is not a return — it is recovering capital with zero profit. If that recovery takes 3 years, your XIRR over those 3 years is approximately 0%, while an index fund would have compounded at ~12–15%.
• Ignoring the concentration effect: Every averaging-down purchase increases your portfolio's exposure to one stock. Model the impact: if the stock falls another 30% after you average down, what does your portfolio look like? If the answer involves forced selling of other holdings or a position above 20–25% of total portfolio, the averaging-down trade is too large.
• Averaging down on a stock you would not buy fresh: The sunk cost of your original purchase should not influence whether you deploy additional capital. Before averaging down, ask: if I had not already owned this stock, would I buy it today at today's price? If no, the additional purchase is emotional capital allocation, not rational investing.
• Using average cost (not FIFO) for your ITR: As above — CBDT Rule 8AA requires FIFO for listed equity. Filing with average cost as cost of acquisition is incorrect and can attract an ITD notice.

See the averaging-down article for the HDFC Bank (worked) vs Yes Bank (destroyed capital) case study and the three-question decision framework in full.