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Create an Excel Model

In this tutorial, you will create a personal project powered by an Excel model and a web app built with the Interface Builder.

The model in this project emulates a savings account.

Create the model​

Let's define the rules of the game.

To begin, open a blank Excel workbook.

Define the initial balance​

  1. In cell B3, enter 500.
  2. Name the cell initialBalance.
  3. To display currency, set the format of the cell to Accounting.

Define the interest rate​

  1. In cell B4, enter 5.
  2. Name the cell interestRate.
  3. Set the format of the cell to Percentage.

Define the time span of the game​

An Excel model must have a range of cells named Time. Epicenter will use this range to iterate through the steps of the simulation.

  1. Create a named range in cells B6 to N6.
  2. Name the range Time.
  3. Enter values 0 through 12.

These values will represent the number of months that have passed since the account was opened.

Allow the user to make transactions​

Create a variable to represent the total amount of transactions on the account in each month.

  1. Create a named range in cells B7 to N7.
  2. Name the range transactionAmount.
  3. Enter the value 0 in each cell of the range.
  4. Set the format for the range to Accounting.

Calculate the account balance​

Now, let's create a variable to hold the monthly balance.

  1. Create a named range in cells B8 to N8.
  2. Name the range Balance.
  3. Set the format for the range to Accounting.
  4. In cell B8, enter =initialBalance. The account has just been opened, and the initial balance hasn't changed.
  5. In cell C8, enter =(B8+B7)*(1+interestRate). This is the new balance after one month, taking into account all transactions that occurred in the first month and the interest rate.
  6. To calculate the balance for the remaining months, click in cell C8 and drag the green frame to include all the cells of the range to N8.

Savings account Excel model

Enable game steps​

Every Excel model must have a cell named Step. This is a counter that gets incremented each time the participant steps through the simulation.

  1. In cell B10, enter the value 0.
  2. Name the cell Step.

What's next?​

In the next chapter, create an application UI for your simulation with the Interface Builder.