Stock Average Calculator — Average Down and Cost Basis

How the average price is worked out

The average cost per share is the total amount spent divided by the total shares bought. Two lots — 100 shares at 50 and another 100 at 40 — cost 9,000 for 200 shares, an average of 45.00 per share. The average always sits between the highest and lowest purchase price, pulled toward whichever lot carries more shares. Buying 50 shares at 120 and then 30 at 95 gives 8,850 across 80 shares, an average of 110.63 — closer to 120 than to 95 because the first lot is larger. Price alone does not set the average; the share count behind each price does just as much work.

The average is the break-even price

A position's break-even is simply its average cost. In the 200-share example above, the share trading at exactly 45.00 makes the holding worth precisely the 9,000 it cost. At the entered current price of 48, the position shows an unrealised gain of 600, or 6.67% on the money invested. This is why a second purchase at a lower price moves the break-even down: the same recovery in the share price crosses the break-even line sooner. What the second purchase does not do is shrink the loss already sitting on the first lot — those shares still cost what they cost.

Averaging down, stated plainly

Averaging down means buying more of a share after its price has fallen. The arithmetic is genuinely favourable in one narrow sense: the blended cost drops, so a partial recovery — not a full one — returns the position to break-even. In the two-lot example, the first purchase at 50 needs the price back at 50 to break even on its own; after the second lot at 40, the whole position breaks even at 45. The trade-off is equally plain: the position size doubles, so every further fall in the price now hits twice as many shares. Averaging down concentrates more capital in the position that has been falling, and whether that fall reflects a temporary markdown or a deteriorating business is a judgement the arithmetic cannot make. A price can keep falling below any average.

Averaging up works the same way in reverse

Adding to a position after a rise pulls the average cost upward. Buying 100 at 40 first and 100 at 50 later produces the identical 45.00 average as the reverse order — the arithmetic is order-independent. Position builders who add into strength accept a higher break-even in exchange for holding more of something that has been rising. The calculator handles both directions with the same three lots; only the sequence of prices differs.

Fees, partial sales, and fractional shares

The calculation here is fee-free. Trading commissions and transaction taxes raise the true cost of each lot, which nudges the real average slightly above the computed one — the effect is small for low-cost brokers and larger for markets with percentage-based transaction duties. Partial sales complicate cost basis in ways that differ by jurisdiction: some tax systems match sales against specific lots, others mandate an average-cost method, and the method changes the taxable gain. This tool reports the simple blended average of what is currently held, which is the figure relevant for break-even; records for tax purposes follow whatever method the local rules require. Fractional shares work fine — the share fields accept whole numbers, so positions with fractional shares can be scaled up (for instance, entering 25 shares for a 2.5-share holding and reading the per-share figures, which are unaffected by scale).

Reading the result alongside other measures

Average cost describes the position, not the investment case. A holding can sit below break-even while the underlying business improves, or above it while the business weakens. The Dollar Return Calculator adds dividends received into the return picture, and the CAGR Calculator converts a multi-year outcome into an annual rate once a position is eventually closed.