Investing
Combine up to three purchase lots and fees to calculate total cost basis, average cost, market value and unrealized gain.
Average cost per unit
$87.00
Total cost basis
$2,610.00
Total quantity
30
Current market value
$3,300.00
Unrealized gain or loss
$690.00
Unrealized return
26.44%
Result comparison
Cost-basis lots
Detailed values use the same assumptions as the summary above.
| Lot | Quantity | Price | Fee | Lot cost |
|---|---|---|---|---|
| 1 | 10 | $100.00 | $5.00 | $1,005.00 |
| 2 | 20 | $80.00 | $5.00 | $1,605.00 |
| 3 | 0 | $0.00 | $0.00 | $0.00 |
Tax basis can require adjustments for splits, reinvestment, wash sales, return of capital and jurisdiction-specific rules not modeled here.
Calculation method
Total cost includes the fees entered for each purchase. Market value equals total quantity multiplied by current price.
Detailed guide
The cost basis calculator adds quantity multiplied by purchase price for each lot, then includes the entered transaction fee. Dividing total cost by total quantity produces an average cost per unit. A current price is optional for calculating market value and unrealized gain.
This page is separated from a trade-preview calculator because its primary task is the accumulated basis of existing lots. It still provides only a mathematical basis. Tax reporting can require corporate-action and account-history adjustments that cannot be inferred from three purchase entries.
Total cost includes the fees entered for each purchase. Market value equals total quantity multiplied by current price.
Unrealized gain is market value minus the calculated cost. Return percentage divides that gain by total cost.
Decision guide
Google results cover average stock price, cost basis, profit or loss, and tax relevance. This calculator summarizes the purchase lots you enter; official tax basis can require adjustments that are outside a simple weighted average.
Multiply each lot’s unit price by quantity, include fees if appropriate, total the costs, and divide by total units. Never average prices alone when quantities differ. Keep enough precision during the calculation and round only the displayed result.
Specific-lot identification, corporate actions, reinvested distributions, wash-sale adjustments, and transferred shares can change reportable basis. Use brokerage records and current tax guidance for filing. The calculator is a planning aid for straightforward purchases.
Cost basis measures invested cost; market value uses the current price. Their difference is an unrealized gain or loss before selling costs and taxes. A lower average after buying more also means greater capital exposure.
Save a baseline, then change only one input at a time: amount, rate, term, or recurring payment. Record the supporting outputs as well as the headline result—contributions, interest, total cost, remaining balance, or target date. This isolates the assumption that actually changes the decision instead of hiding it inside several simultaneous edits.
Do not tune every assumption until the calculator produces a preferred answer. Start with a cautious case, follow with a central case, and treat the favorable case as an upside scenario. A calculator result is not a lender quote, market forecast, or tax determination; actual dates, rounding, fees, contract rules, and required payments must be checked in primary documents.
Keep enough precision in the inputs and round only the output used for a decision. If the estimate supports a transaction, loan, tax calculation, or long-term plan, repeat it with figures from the contract or official statement. Any difference helps identify the assumption that still needs verification.
A split changes quantity and per-share basis without changing total basis. Enter already adjusted quantities and prices.
Each reinvestment may create another lot. Combine only lots whose records you can accurately represent.
Specific identification, FIFO, wash-sale adjustments and return of capital are not decided by this calculator.
Yes. Each entered fee is added to the cost of its purchase lot.
Yes. Quantity fields accept decimal values.
Not necessarily. Compare it with broker records and applicable tax adjustments.
These primary sources explain the rules and concepts referenced by this calculator. The calculation itself uses only the assumptions entered above.
Updated: August 1, 2026
Useful comparisons
Calculate simple ROI or annualized return and profit after monthly contributions.
Find the weighted average across multiple lots and preview the effect of another purchase.
Model equal monthly investments along a smooth price-growth path and estimate shares purchased, average cost and ending value.