Buying more of a position at a different price? See your new average cost, break-even with fees, and the shares needed to hit a target average.
Your average cost is total dollars invested divided by total shares. If you own 100 shares at $50 ($5,000) and buy 50 more at $40 ($2,000), you now hold 150 shares for $7,000, so your average is $46.67. The first calculator does that math and adds any commission to the cost basis, which is how most brokers report it.
The same formula works for averaging up: buy at a higher price and your average rises. Type the real buy price either way.
To pull your average down to a target, you need enough new shares at today’s price. The formula is shares owned × (current average − target) ÷ (target − current price). With 100 shares at $50, a $40 price and a $45 target, that’s 100 × 5 ÷ 5 = 100 more shares, or $4,000. The target must sit between today’s price and your current average; otherwise no number of shares gets you there, and the calculator says so.
A lower average cost doesn’t change what the stock is worth. It only changes your break-even. Buying more of a falling position also increases how much of your account rides on one ticker. Decide how much you’re willing to lose on the whole position first; the position size calculator and the risk/reward calculator help you frame that before you add.
When you close the position, use the stock profit calculator with your average cost as the buy price to see gain, ROI and commission on the whole trade. Taxes depend on your lot method (FIFO, specific ID) and holding period, which this page doesn’t model.
The calculator doesn’t include dividends, splits, wash-sale adjustments or currency conversion. It’s educational math, not investment advice. Check your broker’s cost basis for tax reporting.