Average Up Trade Calculator: Find Your New Cost Basis

An average up trade calculator estimates the new average purchase price per share after you buy more shares at a price above your current average. Enter your existing shares and average price, plus the additional shares and their purchase price, to see the combined share count, total cost, and new average.

Formula

The new average is the combined cost of the shares divided by the total number of shares:

New average price = (Q₁ × A₁ + Q₂ × P₂) ÷ (Q₁ + Q₂)

• Q₁ is the number of shares held before the trade, in shares.
• A₁ is the existing average purchase price, in dollars per share.
• Q₂ is the number of additional shares purchased, in shares.
• P₂ is the price paid for each additional share, in dollars per share.

The resulting average is a weighted average: each purchase contributes according to how many shares it represents. The calculator treats the entered prices as purchase prices and does not include commissions, taxes, dividends, or other adjustments. Enter a positive share quantity for at least one of the two purchases; if both quantities are zero, the average is undefined.

Worked Example

Using the calculator’s default values:

• Existing position: 100 shares at $50 per share = 100 × $50 = $5,000.
• Additional purchase: 50 shares at $60 per share = 50 × $60 = $3,000.
• Combined cost: $5,000 + $3,000 = $8,000.
• Combined shares: 100 + 50 = 150.
• New average: $8,000 ÷ 150 = $53.333…, or $53.33 per share rounded to two decimal places.

The new average is between the old average of $50 and the new purchase price of $60. The calculator reports combined purchase cost as $8,000.00 and total share count as 150.

What an Average Up Trade Means

“Averaging up” means adding to a position at a price higher than its existing average cost. It is the counterpart to averaging down, where additional shares are bought below the existing average. The phrase describes how the purchase changes the cost basis calculation; by itself, it does not establish whether a trade is appropriate or how an investment may perform.

For example, buying 50 shares at $60 after holding 100 shares at an average of $50 raises the average to about $53.33. The result is not the simple midpoint of $50 and $60 because the first purchase involved twice as many shares as the second. A simple midpoint would only apply if the two purchases had equal share quantities.

How to Enter the Numbers

1. Enter the number of shares currently held and the average price per share associated with them.
2. Enter the number of shares in the new purchase and its price per share.
3. Read the new average, combined cost, and total number of shares.

Use the same currency and share units for both purchases. If your holdings came from several transactions, the existing average should represent those holdings using the cost-basis method relevant to your records. The calculator cannot determine that method or recover missing transaction details: it only combines the figures supplied.

You can enter zero for a purchase quantity when you want to represent a position that has not yet been bought. Do not enter zero for both quantities, because there would be no shares over which to calculate an average. The per-share price inputs must be positive in this calculator.

How to Read the Result and Its Limits

The new average is a mathematical summary of the purchase amounts entered; it is not necessarily the same as a broker’s displayed tax or accounting cost basis. Records may reflect transaction fees, corporate actions, reinvested distributions, or a particular method for matching shares sold. Those details are not inputs here. Check the relevant account records when you need an official or complete cost-basis figure.

The combined purchase cost is calculated as the sum of each quantity multiplied by its entered price. It is not a current market value, a profit or loss figure, or an estimate of future returns. To calculate unrealized gain or loss, a separate current price and a clearly defined treatment of costs would be needed. The calculator makes no forecast about share prices.

Common Mistakes and Alternatives

• Taking an unweighted midpoint: Multiply each price by its share quantity before adding; otherwise, differently sized purchases are treated as equal.
• Mixing units or currencies: Both share quantities must use the same unit, and both prices must use the same currency.
• Using a rounded average repeatedly: If possible, use the unrounded underlying total cost and share count for later calculations. Repeated rounding can create small differences.
• Confusing average cost with market price: The new average reflects entered purchases, not the latest quote or the value of the holding today.

If you know the total cost and total share count directly, you can calculate the average as total cost divided by total shares. For more complicated transaction histories, a spreadsheet or account record that includes each lot and relevant adjustments can preserve more detail than a four-input calculator.

Frequently Asked Questions

How do I calculate my average share price after buying more?
Multiply each purchase’s share count by its price, add the resulting costs, then divide by the total shares from both purchases.

Why did my average go up after I bought more shares?
If the new purchase price is above your existing average, the added shares pull the weighted average upward. The size of the change depends on the number of shares in each purchase.

Is averaging up the same as averaging down?
No. Averaging up means buying at a price above the existing average; averaging down means buying below it. Both terms describe the direction of the calculated average, not a prediction of investment results.

Does this calculator include commissions or taxes?
No. It uses only the share quantities and per-share purchase prices entered. Add eligible costs to the underlying cost figures separately if your calculation requires them, and consult the records that apply to your situation.

Can I use it if I have several earlier purchases?
Yes, if you enter an accurate existing share count and average price that summarize those purchases for your intended calculation. For transaction-level or adjusted cost-basis records, retain the individual purchase details.

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in oldqty | Existing shares | shares | 100 | 0 | 100000000
in oldavg | Existing average price | $ | 50 | 0.01 | 100000000
in newqty | Additional shares | shares | 50 | 0 | 100000000
in newprice | Additional purchase price | $ | 60 | 0.01 | 100000000
out avg | New average cost per share | $ | (oldqty * oldavg + newqty * newprice) / (oldqty + newqty) | 2
out cost | Combined purchase cost | $ | oldqty * oldavg + newqty * newprice | 2
out qty | Combined share count | shares | oldqty + newqty | 0