title: Dynamically sum 2 fields on an MVC Edit form
body: <p>I have an MVC Edit form with 2 fields called ExVAT and VAT. I want to add another field with the total of these 2 values. </p>
  
  <p>At the moment what I have shows the total of the 2 fields when the form is loaded. But if you were to change one of the other fields the total is not updated to reflect the new total.</p>
  
  <p>So for example in the screen shot below:</p>
  
  <p><img src="https://i.stack.imgur.com/Cn5sf.jpg" alt="enter image description here"></p>
  
  <p>I have changed the Ex.Vat Figure from 22 to 32, but the total has not been updated (I'll deal with formatting when the value is correct)</p>
  
  <p>The code to get the total is:</p>
  
  <pre><code>@Html.Raw(Model.Vat + Model.ExVat)
  </code></pre>
  
  <p>What is the best way to make the total field update as the other fields are edited?</p>