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Calculating 2 values from fields but it's not working properly

I am calculating 2 fields on a form with values but it seems in some cases it's not working. Here's my javascript. I am adding $oneTimeCostField and $recurringTotalCostField to get the value into the $totalRetailAmountField. Here's the result I am getting when I add say 1,555.00 + 566.00 = the value is 567.00 (?). Any idea what I'm doing wrong? In some cases it works correctly when the values are lower. Thanks, just stumped
var $recurringCostField = $('#am_attribute_campaign_addon_monthly_cost_value');
var $recurringTotalCostField = $('#am_attribute_campaign_addon_total_monthly_cost_value');
var $totalRetailAmountField = $('#am_oie_string_total_monthly_cost_value');
var $oneTimeCostField = $('#am_attribute_campaign_addon_one_time_cost_value');
function calcVal() {
var num1 = $oneTimeCostField.val();
var num2 = $recurringTotalCostField.val();
var result = parseFloat(num1) + parseFloat(num2);
if (!isNaN(result)) {
$totalRetailAmountField.val(result.toFixed(2));
}
}
calcVal();
$oneTimeCostField.on("keydown keyup", function() {
calcVal();
});
$recurringTotalCostField.on("keydown keyup", function() {
calcVal();
});

You need to remove the commas before parsing:
var result = parseFloat(num1.replace(/,/g, '')) + parseFloat(num2.replace(/,/g, ''));
similiar question on this link
Remove commas from the string using JavaScript

That is because parseFloat() converts the string "1,555.00" to the number 1.
To convert it to a proper floating point number, it needs to include a single dot only.
console.log(parseFloat("1.555"));

Why I can't perform the toFixed() function after the sum of 2 retrieved values?

Into a JQuery script I have the following problem trying to use the toFix() JavaScript method on a number.
So I have the following situation:
var anticipoProgetto = $("#valoreAnticipo").text();
var saldoProgetto = $("#valoreSaldo").text();
var anticipoCalcolato = (saldoProgetto + anticipoProgetto);
console.log("ANTICIPO CALCOLATO: " + anticipoCalcolato);
anticipoCalcolato = anticipoCalcolato.toFixed(2);
$("#anticipoModaleUlterioreSaldo").val(anticipoCalcolato);
The console.log() show:
ANTICIPO CALCOLATO: 2192.002200.37
So it means that JavaScript have correctly perform the addition.
The problem is that wehn try to perorm this line to obtain a value with only 2 decimals digits:
anticipoCalcolato = anticipoCalcolato.toFixed(2);
in the FireBug console I obtain this messagge error:
TypeError: anticipoCalcolato.toFixed is not a function
anticipoCalcolato = anticipoCalcolato.toFixed(2);
Why? What am I missing? How can I fix this issue?

The math is wrong because you are adding two string together, not two numbers. And he toFixed error is because you are trying to use toFixed on a string, but that ethod only exists on numbers.
Convert the strings to numbers when you read the .text()
var anticipoProgetto = parseFloat($("#valoreAnticipo").text()),
saldoProgetto = parseFloat($("#valoreSaldo").text()),
anticipoCalcolato = anticipoProgetto + saldoProgetto,
fixed = anticipoCalcolato.toFixed(2);

#espacarello is correct, you need to cast from string to number. It may be more to your intent to cast them as you read them.
If #valoreAnticipo is an input element, consider switching to .val() instead of .text()
var anticipoProgetto = parseFloat($("#valoreAnticipo").text()) || 0;
var saldoProgetto = parseFloat($("#valoreSaldo").text()) || 0;
var anticipoCalcolato = (saldoProgetto + anticipoProgetto);
console.log("ANTICIPO CALCOLATO: " + anticipoCalcolato);
anticipoCalcolato = anticipoCalcolato.toFixed(2);
$("#anticipoModaleUlterioreSaldo").val(anticipoCalcolato);

Convert comma's into periods js

So I'm trying to make a calculation but it obviously wont calculate with ',' in the numbers. I want to change these vars and make the ',' into '.' using javascript
oldSum.value = '48,35'
newSum.innerHTML = '€43,40'
var oldSumPre = oldSum.value;
var oldStripped = oldSumPre.replace(/,/g, ".");
var newSumPre = newSum.innerHTML;
var newStripped = newSumPre.replace(/,/g, ".");
bedrag.innerHTML = oldStripped - newStripped;
Is what Im doing right now.. but it changes bedrag.innerHTML into NaN

var str = "R,e,p,l,a,c,e";
var res = str.replace(/,/g, ".");
alert (res);

Suppose your variable is vNum. You need to replace all commas with '.' using this
vNum = vNum.replace(",", ".");

In general you could use a localization / internationalization library, which will solve some other tasks you are likely to run into as well.
For example this one:
https://github.com/jquery/globalize/blob/master/doc/api/number/parse-number.md
Snippet:
Globalize.locale( "es" );
Globalize.parseDate( "3,14" ); // 3.14

Addition not working in Javascript

I'm really new to Javascript and trying to create a form where I'm running into some trouble...
When I use + it does not add up to the value, instead it just puts it back to back. Ex: 5+10 (510)
Here's my code if you want to take a look at it. I'd appreciate any help since I can't figure this out on my own.
var service = document.getElementById("service");
var serviceprice = service.options[service.selectedIndex].id;
var tech = document.getElementById("tech");
var techprice = tech.options[tech.selectedIndex].id;
var hours = document.getElementById("hours").value;
// The error happens here
var total = techprice * hours + serviceprice;
I also have an html part which the script gets the data from.

That happens whenever you have a string rather than a number. The + operator performs concatenation for strings. Make sure you parse your strings to numbers using parseFloat or parseInt:
var service = document.getElementById("service");
var serviceprice = parseInt(service.options[service.selectedIndex].id, 10);
var tech = document.getElementById("tech");
var techprice = parseInt(tech.options[tech.selectedIndex].id, 10);
var hours = parseInt(document.getElementById("hours").value, 10);
Note that parseInt takes an argument to specify the base. You almost always want base 10.

Try changing this line:
var total = techprice * hours + serviceprice;
to
var total = techprice * hours + parseFloat(serviceprice);
I suspect 'servicePrice' is a string, and it will then try to concatenate the first value (let's say: 100) with the second value (which is, not a number, but a string, let's say 'test'), the result being '100test'.

Try to convert the string to int first with parseInt or to float with parseFloat

This is not especially elegant, but I find it simple, easy, and useful:
var total = -(-techprice * hours - serviceprice);
or even:
var total = techprice * hours -(-serviceprice);
They both eliminate the ambiguous + operator.

My VAT calculation is wrong

I'm trying to do a function for making a small calcul with vat.
So I have the following code:
<script type="text/javascript">
function calcdebours()
{
var taux = document.getElementById('debours_taux_tva').value;
var ht_no_tva = document.getElementById('debours_montant_ht_no_tva').value;
var ht_tva = document.getElementById('debours_montant_ht_tva').value;
var tva= Math.round((((ht_tva)*(taux))/100)*100)/100;
;
if(taux=='')
{
taux=0;
}
if(ht_no_tva=='')
{
ht_no_tva=0;
}
if(ht_tva=='')
{
ht_tva=0;
}
document.getElementById('debours_montant_tva').value = tva ;
document.getElementById('debours_montant_ttc').value = (tva) + parseInt(ht_tva)+ parseInt(ht_no_tva)
}
</script>
And below the fiddle:
http://jsfiddle.net/6zzRZ/
But for all it make the wrong calculation, I think it does not count the cent.
I've tried using just var 1 + var 2 but it just used to concatenate the number sor I use the parseInt function.
It has worked but the result is wrong for any kind of amount.
The trouble is that I tried parseDecimal but it say that this function does not exist.
Any kind of help will be much appreciated.

Try parseFloat. Or use the unitary + like this: var ht_no_tva = +document.getElementById('debours_montant_ht_no_tva').value; This gives JavaScript the hint that it should treat the value as a number.

Use parseFloat() instead of parseDouble:
http://www.w3schools.com/jsref/jsref_parsefloat.asp