Stock Average Calculator

The Stock Average Calculator is a stock average calculator that combines multiple purchases of the same stock or cryptocurrency into one weighted average cost per share: enter each purchase lot (shares and price), an optional per-trade brokerage fee, and an optional current price, and it returns your total shares, total invested, average cost, and, with a current price entered, your unrealized profit or loss and percentage return.

How It Works

Each lot contributes shares x price. The calculator sums lots, adds the brokerage fee once per lot, and divides the total cost by the total shares:

$\text{Average price}=\frac{\sum(\text{Shares}\times\text{Price})+(\text{Fee}\times\text{Lots})}{\sum\text{Shares}}$

Only lots with both shares and price above zero are included. Share counts accept decimals, which is what makes the same tool work for fractional-share brokers and crypto purchases.

Parameters

| Input | Required | Meaning | |---|---|---| | Shares per lot | Yes | Quantity bought in each purchase (decimals allowed) | | Price per lot | Yes | Price paid per share in that purchase | | Brokerage fee | No | One fee amount, applied once per lot | | Current price | No | Unlocks current value, unrealized P&L, and return % |

Worked example

You buy 10 shares at $100 and later 20 shares at$80, paying a $5 fee per trade. The lots cost$1,000 and $1,600, fees add$10, so total cost is $2,610 across 30 shares: an average price of **$87.00**. At a current price of $90 the position is worth$2,700, an unrealized profit of **$90, about +3.45$87, not the $90 a simple mean of the two prices suggests, because the cheaper lot was twice as large; and the$87 already includes fees, so it is a true break-even, the price at which selling recovers everything you spent, before taxes and exit costs.

Averaging down, honestly

This calculator is the bookkeeping heart of the averaging-down strategy: buying more as a price falls so the break-even falls faster than the price does. The mathematics genuinely works, each cheaper lot drags the average toward it in proportion to its size, which is why doubling down at $80 moved the example's break-even by$13 while the first lot alone sat at $100. The strategy's risk is equally mathematical: the average converges toward the price of a falling asset while your exposure grows, so a position can be "closer to break-even" and far larger in dollars lost if the decline continues to zero. Averaging down is a sizing decision about a thesis you still believe, executed in lots; the calculator keeps the cost side exact so the decision is made on facts, and the per-lot view it preserves matters later for tax, where each lot keeps its own purchase date and basis in most jurisdictions' records.

Reading the return figure

The percentage return is unrealized P&L divided by total cost, fees included, which makes it slightly stricter than broker displays that quote return on invested capital excluding fees. It excludes dividends received along the way (add them mentally to the P&L for a total-return view), distributions, and any interest or FX movement for overseas holdings. For crypto positions the same framing holds, with the practical addition that prices are continuous and volatile enough that the current price you enter is stale within minutes; the average cost, not the momentary return, is the durable output of the tool.

Limitations

Purchases only: the calculator does not process sales (which would require a cost-basis method, FIFO, LIFO, or specific-lot, and changes the average in method-specific ways), dividends, splits (enter post-split share counts and prices consistently), wash-sale or tax-lot rules, or currency conversion. The single fee amount is applied uniformly to every lot, so mixed-fee histories should be entered as separate runs or with an average fee. It computes cost basis for planning; your broker's official cost-basis statement governs taxes.

Frequently Asked Questions

Why is the average not just the mean of my purchase prices?

Because lots have sizes. A mean weights every price equally; your money weights every share equally, and a 100-share lot should move your break-even ten times more than a 10-share lot. The weighted average is the only figure whose multiplication by total shares returns your actual total cost.

Does the current price change my average cost?

No. Average cost is history; it is fixed by what you paid. The current price only values the position against that history, producing the unrealized profit or loss and the return percentage.

Can I use this for crypto and fractional shares?

Yes. Shares accept decimals, so 0.25 BTC at one price and 0.1 BTC at another average exactly like share lots. Enter any per-trade exchange fee in the fee field so the break-even includes it.