Javascript not running, does nothing

Hi all, 

I need some help please, I'm doing a form were if you buy something over a certain amount it triggers a 24 month payment plan option and if you go over the next amount it triggers a 36 month plan as well. I've written some code using the IF command for the first time, it says there are no errors but when I add an amount a hit the button to run the calcucations it does nothing.

I've attached a screengrab of the form, how the boxes are formatted and the code is worded (below)

var total = this.getField (‘TotalValue’);

var IFCdeposit = this.getField (‘_IFCdepositsum’);

var IFCsum = this.getField (‘_IFCtermsum’);

var IFC24 = this.getField (‘_24IFCmonthly’);

var IFC36 = this.getField (‘_36IFCmonthly’);

if (total.value >= 12000.00) IFCdeposit.value = total.value * 0.50;

var IFCdepositCalc = total.value * 0.50;

IFCdeposit.value = IFCdepositCalc;

IFCsum.value = IFCdepositCalc;

if (IFCsum.value >= 6000.00)

var IFC24Calc = IFCsum.value / 24;

IFC24.value = IFC24Calc;

if (IFCsum.value >= 7500.00)

var IFC36Calc = IFCsum.value / 36;

IFC36.value = IFC36Calc;

Any help would be greatfully recieved, as I'm no coder......

Thanks Simon