How to use it
Add a row for each time you bought the stock: the number of shares and the price you paid. The calculator keeps a running weighted average cost, your total shares, and your total invested. Add as many lots as you need, and remove any row you entered by mistake.
How weighted average cost works
Your average cost isn’t a simple average of the prices you paid — it’s weighted by how many
shares you bought at each price. The formula is
average = (Σ shares × price) ÷ (Σ shares). Buy 100 shares at $50 and 50 at $42 and
your average isn’t $46; it’s ($5,000 + $2,100) ÷ 150 = $47.33, because the $50
lot carries twice the weight of the $42 lot.
Why exact math matters
Cost-basis math done with ordinary floating-point arithmetic can drift by fractions of a cent, which looks wrong on a position summary. TradeCaliper computes every average with exact decimal arithmetic, so what you see is what the numbers actually are.
TradeCaliper is a planning and education tool, not financial advice.