Cost basis

Cost basis is what a holding originally cost you, carried forward across every purchase you made in it. Buy the same share three times at three prices and there is no single purchase price left, so a method is needed to combine them. The average cost method divides the total amount invested by the number of shares held, which produces one figure per position.

Why it matters

Every profit number you read is a difference between today's value and this base, so the method quietly decides what your gain looks like. Brokers do not all use the same one, and they differ again on whether transaction fees sit inside the basis or are booked separately, which is the usual reason a tracker and a broker app disagree by a few euros on the same position. Knowing which convention produced a number is the difference between spotting an import error and chasing a ghost.

How BullBenchmark shows it

We use average cost and book fees separately, and the position shows the share count and the average price we derived from your transactions. Clicking a position opens the transactions behind it, so a figure that does not match your broker can be traced to the row that caused it rather than argued about. The positions table with its cost column is open on the demo portfolio, no upload required.

Related terms

Realized and unrealized gains · Market value · Stock split

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