Purchase 2 priceHigh modeled impact
Higher input raises the modeled result
Each lot price is weighted by its quantity.
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Average Cost / Cost Basis Calculator
Combine purchase lots to estimate total cost basis and average cost per unit.
Your result
Average cost per unit
—
Total cost basis—
Total quantity—
Through the Lens
What drives this result?
Controlled, deterministic sensitivity around your current inputs reveals which assumptions move the average cost per unit most.
Purchase 1 priceLow modeled impact
Higher input raises the modeled result
Each lot price is weighted by its quantity.
Purchase 2 quantityLow modeled impact
Higher input raises the modeled result
Quantity changes how much influence the second lot has.
Purchase 1 quantityLow modeled impact
Higher input lowers the modeled result
Quantity changes how much influence the first lot has.
Entered feesLow modeled impact
Higher input raises the modeled result
Fees add to total cost before division by total units.
High modeled impact means an input changes this output substantially around the current scenario. Rankings compare controlled 10% input changes; they do not measure risk, probability, personal importance, controllability, suitability, advice, or forecasts.
Meaning
What this means
Meaning
Average cost is total cost basis divided by total units. It gives a useful break-even reference before taxes or future selling costs.
Implication
The weighted average gives a unit-level cost reference. It is not necessarily the tax basis recognized by a tax authority when account adjustments or lot-selection rules apply.
Formula and methodology
How the calculator works
Lot cost
quantity × purchase price + entered feesTotal cost basis
sum of all lot costsAverage cost per unit
total cost basis ÷ total quantityThe two entered purchase lots are combined. The single fee input is included once in total cost. Money is displayed to two decimals for average cost and whole currency units for total cost.
Cost basis explained
How to calculate average cost
Weight each purchase by its quantity
Multiply each lot’s units by its purchase price, add the purchase costs and any entered fees, then divide by the total units. For 10 units at $20 and 30 units at $40, the total is 40 units costing $1,400; the average cost is $35.00 per unit with no fees entered.
A simple average of $20 and $40 would be $30, but it gives the smaller and larger lots equal weight. With 10 and 30 units, the weighted result is $35. The single fee field on this calculator is added once to total cost before division.
Average cost versus cost basis
Here, cost basis means the combined purchase costs plus the entered acquisition fee; average cost is that modeled total divided by units. Tax basis may differ. In Canada, adjusted cost base (ACB) can require adjustments beyond these two lots and one fee; rules also vary by account and jurisdiction.
Use this as an educational purchase-cost reference, not an official tax calculation or advice on which lots to sell.
Assumptions and limitations
What the scenario includes—and leaves out
Assumptions
- Both purchases are of the same asset and use the same currency.
- Entered fees are acquisition costs that should be included in the scenario basis.
- Quantities and prices have already been adjusted for any splits or reorganizations.
Limitations
- Selling costs, taxes, foreign exchange, distributions, corporate actions, and jurisdiction-specific basis adjustments are excluded.
- The result does not select tax lots or establish an official tax basis.
- No broker or exchange data is fetched.
Educational scenario only. Results are modeled estimates, not forecasts or personalized financial, investment, legal, or tax advice.
Known-answer checks
Examples used to validate the engine
Weighted average10 units at 20 and 30 units at 40 produce a total cost of 1,400 and average cost of 35.
Fees includedA 20 fee raises the same example’s total cost to 1,420 and average to 35.50.
Decimal unitsPositive fractional quantities are accepted.
Invalid lotZero quantity, negative price or fees, and non-finite values are rejected.
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