This is "By Design". The parseFloat function will only consider the parts of the string up until in reaches a non +, -, number, exponent or decimal point. Once it sees the comma it stops looking and only considers the "75" portion.

• https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/parseFloat

To fix this convert the commas to decimal points.

var fullcost = parseFloat($("#fullcost").text().replace(',', '.'));

You need to replace (remove) the dots first in the thousands separator, then take care of the decimal:

function isNumber(n) {
    'use strict';
    n = n.replace(/\./g, '').replace(',', '.');
    return !isNaN(parseFloat(n)) && isFinite(n);
}

parseFloat works with decimals only, but you could replace commas to decimal points in the incoming number:

let commafreeNumber = value.replace(/,/g, '.')

If the incoming number already contains decimal points (e.g. 1.234,56) you can remove them before changing the commas:

number.replace(/\./g, '').replace(/,/g, '.')

Your answer is close, but not quite right.

replace doesn't change the original string; it creates a new one. So you need to create a variable to hold the new string, and call parseFloat on that.

Here's the fixed code:

function parseFloatIgnoreCommas(number) {
    var numberNoCommas = number.replace(/,/g, '');
    return parseFloat(numberNoCommas);
}

I also renamed the function to parseFloatIgnoreCommas, which better describes what it does.