jquery calculate

HTML

<form class="form-horizontal" id="whereEntry" method='post' action=''>
       <fieldset>
        <input type="text" class="income_count span1 register_input" id="income" name="income" placeholder="% of income"> <br>
        <input type="text" class="income_count span1 register_input" id="income_2" name="income_2" placeholder="% of income"> <br>
<input type="text" class="income_count span1 register_input" id="income_3" name="income_3" placeholder="% of income"> <br>
    <input type="text" class="income_count span1 register_input" id="income_4" name="income_4" placeholder="% of income"> <br>
        <input type="text" class="income_count span1 register_input" id="income_5" name="income_5" placeholder="% of income"> <br>
            <input type="text" class="income_count span1 register_input" id="income_6" name="income_6" placeholder="% of income"> <br><br><br>
                                
       <input type="text" class="span2 register_input" id="income_sum" name="income_sum" placeholder="% of income"> <br>
           </fieldset>
           </form>

CSS

@import url('http://twitter.github.com/bootstrap/assets/css/bootstrap.css');

JavaScript

var $form = $('#whereEntry'),
    $summands = $form.find('.income_count'),
    $sumDisplay = $('#income_sum');

$form.delegate('.income_count', 'change', function ()
{
    var sum = 0;
    $summands.each(function ()
    {
        var value = Number($(this).val());
        if (!isNaN(value)) sum += value;
    });

    $sumDisplay.text(sum);
});