Equal cash purchases buy unequal BTC quantities
Dollar-cost averaging means investing a fixed amount at regular intervals, as described by Investor.gov. Applying the arithmetic to BTC, a lower purchase price buys more units with the same spending budget. This changes the weight of each price in your average; it does not guarantee a profitable investment.
For an illustrative example without fees, spend 300 USDT at 60,000 USDT per BTC, 300 USDT at 50,000, and 300 USDT at 75,000. The three purchases deliver 0.005 BTC, 0.006 BTC and 0.004 BTC. Total spending is 900 USDT and the quantity is 0.015 BTC, so average acquisition cost is exactly 60,000 USDT per BTC.
Why averaging the displayed prices gives the wrong answer
The simple arithmetic mean of 60,000, 50,000 and 75,000 is 61,666.67. That would be appropriate if you bought equal BTC quantities at each price. It does not describe this equal-spending example. The second purchase contributes the largest quantity, so its lower price deserves the greatest quantity weight.
The general formula is sum of each purchase's price multiplied by its BTC quantity, divided by total purchased BTC. It also works when spending amounts vary. In practice, use actual filled quantities and spending from trade records instead of an order's requested quantity, since an order can fill through several trades or only partially.
Choose one fee convention and apply it consistently
Suppose each of the example purchases also incurs a separate 1 USDT fee paid on top of the 300 USDT purchase value. The BTC total remains 0.015, while total included spending becomes 903 USDT. The arithmetic acquisition cost including those fees is therefore 60,200 USDT per BTC.
If a fee is deducted in BTC, the net acquired quantity is smaller instead. If the total debit is fixed and includes the fee, less than the full debit buys BTC. These are different input cases. Record the fee asset and whether the amount is included in spending; otherwise the same fee can be counted twice. Coinbase's fills documentation provides separate execution price, size and fee fields as one example of useful source records.
Distinguish acquisition cost from the price needed to exit
With 903 USDT of included acquisition spending and 0.015 BTC available to sell, an assumed 0.10% sale fee raises the illustrative break-even sale price to 903 / (0.015 × 0.999): approximately 60,260.26 USDT. This assumes no other sale cost and a full fill at one effective price.
Transfers between your own wallets are not additional purchases in this arithmetic ledger. Reconcile quantities so an exchange withdrawal and wallet deposit do not duplicate holdings. Sales, rewards and missing history require additional record treatment. This calculator's weighted acquisition cost is a portfolio arithmetic measure; it does not select a tax-lot method or determine the taxable basis required by your jurisdiction.
Questions about this tool
Can DCA reduce my average price while I am still losing money?
Yes. A new purchase below the previous average can reduce that average, while the market remains below the new acquisition cost. It also increases the amount committed to BTC.
Should I enter an exchange order or each individual fill?
Individual fills give the clearest record. An order-level entry is sufficient if its quantity, effective average fill price and fees accurately reconcile to those fills.