JavaScript Stock Profit Calculator

5 minute read

JavaScript Stock Profit Calculator


A JavaScript library for calculating the gain / loss of stock market transactions.

I started trading last 2014 to learn more about investing. My colleague helped me by providing references and tools. One of the tools is a stock profit calculator made in MS Excel. I thought of creating a stock market application for Android before but did not have the time to finish it. Instead, I extracted the code of the stock calculator and created this project.

Feel free to raise any suggestion / concern. I hope this library can help others.


  • Simple API
  • Dynamic Stockbroker Creation
  • Customizable Transaction Fees
  • Uses BigNumber of Math.js
  • Transaction Fee Breakdown

Getting Started

  1. Import the JavaScript files.

     <!--  Dependencies -->
     <script src=""></script>
     <!-- Core library files -->
     <script src="broker.js"></script>
     <script src="stock.calculator.js"></script>
     <!-- [Optional] -->
     <script src="brokers/broker-col.js"></script>
    • Dependencies:
    • Core library files:
      • broker.js - contains the Broker class.
      • stock.calculator.js - contains the StockCalculator class.
    • Optional files:
      • broker-col.js - contains the Broker implementation for COLFinancial named as ColBroker.
      • Note: As of the moment, this is the only pre-created broker available.
  2. Create a custom / use a pre-created stockbroker.

     var broker1 = new Broker("Broker Name"); // Create a new broker instance
     var broker2 = window.ColBroker; // Or use the default instance
  3. Add transaction fees to broker instance.

       name: 'commission',
       descrip: 'Commission',
       handler: function() { 
         return 'max(0.0025 * grossTradeAmt, 20)'; 
     }, FeeType.BUY, FeeType.SELL);
    • Broker#addFee( feeObj, feeType... ) function accepts at least two parameters.
      • Fee
        • name - The variable name of the transaction fee that can be used by other fee handlers during evaluation.
        • descrip - The description of the transaction fee.
        • handler - A function that returns a String to be evaluated by Math.js.
      • Fee Type(s)
        • BUY
        • SELL
      • Note: grossTradeAmt is the default available variable for fee handlers.
  4. Create an instance of the calculator.

     var calc = new StockCalculator( broker );
  5. Compute gain / loss.

     calc.compute( 8000, 1.35, 1.40);
    • StockCalculator#compute(noOfShares, buyPrice, sellPrice [, showDetails]) function requires three parameters.
      • noOfShares - The total number of shares involved in the transaction.
      • buyPrice - The price of the stock bought.
      • sellPrice - The price of the stock sold.
      • showDetails - [Optional] - A boolean flag that indicates whether transaction fee breakdown will be included or not. Default is false.
  6. Check the results.

       "gain" : 279.1,
       "gainPercent" : 2.5766581178117147,
       "actualBuy" : 1.3539825,
       "actualSell" : 1.38887

    For the detailed result, click here to view it. (Extracted it to a separate link due to its verbosity.)

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