Having trouble getting javascript to calculate fields

I have tried a couple different ways and I feel like this one is the closest to working, however it is not working. I was hoping that someone could point out and explain what I am doing wrong. I think that parseFloat could be my issue, but I am not sure.

window.onload = function () {
    var purchPrice = document.getElementById('purchPrice');
    var warrMile = document.getElementById('warrMile');
    var currentMile = document.getElementById('currentMile');
    var purchMile = document.getElementById('purchMile');
    var mileAdjPerct = 0;
    var mileAdjEach = 0;
    var mileAdjTotal = 0;   
}

function warrUpdate() {
    var warrPerct = (parseFloat(currentMile.value) - parseFloat(purchMile.value)) / parseFloat(warrMile.value);
    var warrEach = parseFloat(purchPrice.value) * warrPerct;
    var warrTotal = warrEach * 4;

    parseFloat(document.getElementById('mileAdjPerct').value = warrPerct);
    parseFloat(document.getElementById('mileAdjEach').value = warrEach);
    parseFloat(document.getElementById('mileAdjTotal').value = warrTotal);
}

Here is a fiddle: http://ift.tt/17yJlLS