基于计算的自动更新字段

Question

I need some help coding a php calculator.. The Algorithm is a little complicated and I would like for the 3rd "Payment" field to auto-update with the result..

The math goes like this: **$payment**=SUM(**$balance***0.0435)/12+(**$credit***0.0025)/12

(This algorithm outputs a Secured LOC Payment for a Mortgage)

So I am needing help calculating the $payment value via php for a web-page. Also I would like for the $payment field to auto-update with the calculated total..

Here is a excel document doing exactly what I need to create for the web: http://www.dev.jomilla.net/FNCals/SCFC_Secured%20LOC%20Payment%20Calculator_2013%2005%2023.xlsx

My Fields are written as

<form>
<input name="credit" id="credit" type="text" >
<input name="balance" id="balance" type="text" >
<input name="payment" id="payment" class="form-control">
</form>

Please help me calculate and auto-populate the result.. Any help would be greatly appreciated!

I've tried several different ways but I cant seem to make it work, I know some php and js, but I mostly just do front-end web design..

If it helps, my page can be viewed here ..

Answer 1

$("#balance,#credit").blur(function() {
    var b = $("#balance").val();
    var c = $("#credit").val();
    if ('' == b || '' == c) {
        return;
    }
    b *= 0.0435;
    c *= 0.0025;
    b /= 12;
    c /= 12;
    var p = b + c;
    $("#payment").val(p);
});

Note that this can be written in a shorter way, but this is the easiest to understand. Also note that there is no error checking, so if someone writes "foo" in the credit box it's going to break.

A quick fiddle: http://jsfiddle.net/Q9cYv/ shows that the results match up with your Excel file.