How to subtract a percentage from a number in Javascript? -

here code subtracts 2 var.

function calculate() {          var mybox1 = document.getelementbyid('ax').value;            var mybox2 = document.getelementbyid('by').value;         var myresult = mybox1 * mybox2;         var mybox3= document.getelementbyid('mybox3');           mybox.value = myresult ;          } 

this take out percentage.

function calculate() {             var mybox1 = document.getelementbyid('ax').value;                var mybox2 = document.getelementbyid('by').value;             var myresult = mybox1 * mybox2;             var mybox3= document.getelementbyid('mybox3');               var percentage = myresult/mybox3 -2%;             mybox3.value = myresult ; } 

you have several problems in code, apart mixin between subtract , multiplication:

• in first function using mybox undefined should use mybox3 instead.
• and in second function, dividing number input type should replace myresult/mybox3-2 myresult/(mybox3.value-2), append % sign need use +"%".
• in end of second function mybox3 value should take percentage , not result variable.
• don't use same name calculate 2 functions.

this updated code:

function calculate1() {    var mybox1 = document.getelementbyid('ax').value;   var mybox2 = document.getelementbyid('by').value;   var myresult = mybox1 * mybox2;   var mybox3 = document.getelementbyid('mybox3');   mybox3.value = myresult;  }  function calculate2() {   var mybox1 = document.getelementbyid('ax').value;   var mybox2 = document.getelementbyid('by').value;   var myresult = mybox1 * mybox2;   var mybox3 = document.getelementbyid('mybox3');   var percentage = myresult / (mybox3.value - 2) +" %";   mybox3.value = percentage; } 

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edit:

if want subtract 2% multiplication result should calculate value of 2% first, subtract result:

function calculate() {     var mybox1 = document.getelementbyid('mybox1').value;        var mybox2 = document.getelementbyid('mybox2').value;     var myresult = mybox1 * mybox2;     //2% of myresult ===> myresult × 2 ÷ 100     var substpercentage = myresult*2/100;     console.log(substpercentage);     var mybox3 = document.getelementbyid('mybox3');      var percentage = myresult - substpercentage;     mybox3.value = percentage; } 

this the updated fiddle.