How can I reduce 2.5% of the val of the writing box?

I want to reduce the 2.5% of the value in the writing box. this is html code :

    <div class="ZakatCalc">
        <div class="calcimg">
<img src="" alt="" srcset="" class="zcimg">
        </div>
        <div class="clacbox">
<input type="text" name="" class="zcbox">
        </div>
        <div class="calcbtn">
<button class="zcbtn">احسب</button>
        </div>
        <div class="calcresult"></div>
    </div>

this is js code :

var numbox = document.querySelector(".zcbox");
var crus = document.querySelector(".calcresult");

crus.innerHTML = "<p class='numbzkat'>" + Math.floor(numbox.value) - 2.5/100 + "</p>" + "<br/>" + "<p class='zkatnum'>" + "" + "</p>"

I want to calculate this process and then put it between html stacks by innerhtml in the form of a number.

Answer

-2.5% means that you want to get 97.5% of base price.

Math.floor(numbox.value) * .975

Your code calculate base price - 0.025 which isn’t what you want. There are no percentages, just 0.025.