Stock Average Cost After Buying More Calculator

How to use this stock average cost after buying more calculator

1. Existing shares: enter the quantity in count. The worked example uses 100.
2. Existing cost per share: enter the amount in your selected currency. The worked example uses $50.00.
3. Additional shares: enter the quantity in count. The worked example uses 50.
4. New purchase price per share: enter the amount in your selected currency. The worked example uses $40.00.
5. New transaction fee: enter the amount in your selected currency. The worked example uses $5.00.

Start with figures from the same statement date or planning period. Calculate once, save scenario A, then change one assumption to understand its effect. The comparison shows B minus A; a positive difference means the result increased, which is not automatically better.

Formula and calculation method

Average cost = (existing shares × existing cost + new shares × new price + new fee) / total shares.

The calculator evaluates this relationship directly in your browser. The displayed precision is for readability and does not imply a guaranteed outcome. Time periods and rate conventions matter: use the exact units in each input label and avoid mixing monthly and annual values.

What the result means

Averaging down lowers the cost per share only when the new purchase is sufficiently cheaper. It also increases exposure to the same investment and does not reverse an economic loss.

Two worked examples

1. Illustrative planning scenario

Existing shares = 100; Existing cost per share = $50.00; Additional shares = 50; New purchase price per share = $40.00; New transaction fee = $5.00.

Apply the stated formula with these inputs. Monetary examples use USD; percentages are divided by 100 inside the calculation. Intermediate calculations retain full precision and displayed amounts are rounded.

2. Simplified calculation check

Existing shares = 10; Existing cost per share = $100.00; Additional shares = 10; New purchase price per share = $50.00; New transaction fee = $0.00.

Apply the stated formula with these inputs. Monetary examples use USD; percentages are divided by 100 inside the calculation. Intermediate calculations retain full precision and displayed amounts are rounded.

The second example uses simpler inputs to make the arithmetic easier to check. It is also included in the automated regression suite. These examples illustrate the model and are not market averages, live offers or personalized advice.

Assumptions and limitations

Existing per-share cost should already include prior fees. No share sales, splits, currency conversions or tax-lot accounting. Fractional shares are permitted.

Use this output to frame a question or compare consistent scenarios. Reconcile any decision involving an actual product, employment agreement or financial statement with its underlying documents. If a contract uses different rounding or timing, its result may differ from this estimate.

Frequently asked questions

Sources and verification

The following primary sources provide background on the financial concepts. CalcPane’s formula and assumptions above define this specific model; these organizations do not endorse CalcPane or certify its outputs.

• Investor.gov — Compound interest calculator
• Investor.gov — How fees and expenses affect a portfolio

Formula implementation and worked examples checked by automated tests on 2026-10-17. Inspect this calculator’s inputs and expected outputs. Read our calculation methodology. Independent professional review has not been completed for this release.

Cite this calculator

CalcPane. (2026-10-17). Stock Average Cost After Buying More Calculator. https://calcpane.com/stock-average-cost-two-purchases-calculator/

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