JS/jQuery finance calculator
You have cached the selectors beforehand,

// we need to cache selectors to avoid re-reading the DOM
 var amount = $("#amount"),
     duration = $("#duration"),
     interest = $("#interest"),
     income = $("#incomeNeeded"),
     monthlyRate = $("#monthlyRate");


So why not use them here,

$("#amount").val($("#slider-range-min").slider("value") + " $$$");


and

slide: function (event, ui) {
     $("#amount").val(ui.value + " $$$");


to 

amount.val($("#slider-range-min").slider("value") + " $$$");


and 

slide: function (event, ui) {
     amount.val(ui.value + " $$$");


Repeat similarly for #duraton and #interest.



Also, instead of using .slice(x,y) where x and y are static values, why not use:

.slice(0,amount.val().indexOf(' '))


or use split()  - Fiddle

JSPerf test- split vs slice vs substring