Cost Basis Calculator
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Current Price
Result
What is Cost Basis?
The average cost basis is the weighted average price of all purchases of a position, including fees. It is important for calculating gains and losses as well as for tax purposes.
Cost Basis = Total Invested / Number of Shares
What does this tool calculate?
The cost basis calculator determines your average purchase price when you have bought a position in multiple tranches. It optionally includes transaction fees and immediately shows the breakeven price — a prerequisite for any tax calculation and exit decision.
Formula & methodology
| Variable | Bedeutung / Meaning |
|---|---|
| Σ(Stückzahl × Kaufpreis) | Summe aller Kaufbeträge inkl. Gebühren |
| Σ Stückzahl | Gesamtzahl aller erworbenen Anteile |
| Ø Einstand | Σ(Stückzahl × Kaufpreis) ÷ Σ Stückzahl |
Worked example
Kauf 1: 100 Aktien @ $50 = $5.000 · Kauf 2: 100 Aktien @ $60 = $6.000. Gesamt: $11.000 ÷ 200 Aktien = $55 durchschnittlicher Einstand. Gebühren von z.B. $10 erhöhen den Einstand auf $55,05 je Aktie.
When do I use it?
After every additional purchase (averaging down or up) and for your tax return: your broker often shows only the last purchase price or the FIFO basis. The average cost basis is what tells you exactly when you are profitable. Also use it after booking in option premiums (e.g. Wheel strategy).
Frequently asked questions
FIFO vs. average cost — which method does my broker / tax authority use?
In the US, brokers typically use the average cost method for mutual funds and FIFO for individual stocks by default, though you can often elect specific identification. In Germany (Privatvermögen) the tax authority uses FIFO by statute (§ 20 EStG). This matters when older lots have a different cost basis. This calculator shows the weighted average cost — for FIFO-exact tax figures always use your broker's tax statement or consult a tax advisor.
How do I factor in option premiums for the cost basis?
In a Wheel strategy (Cash-Secured Put → Assignment → Covered Call): the premium you collected on the CSP reduces your effective cost basis. Example: assigned at $50 strike after collecting $2 CSP premium → effective cost basis $48. Enter $48 as the purchase price. Covered call premiums further reduce the basis or are treated as current income depending on your tax model — consult a tax advisor for the exact treatment.