为什么我的号码是0

我正试图制作一个计算器来计算在一定时间内燃烧的卡路里量，但每当我运行它时，我都会得到0作为输出。我曾尝试将calorieCountOut变量设置为任意数字，然后它运行得很好，但每次用这里的代码运行它时，我都会得到0。这是我的代码：

const AGECONST = 0.2017;
const WEIGHTCONST = 0.09036;
const HRCONST = 0.6309;
const SUBTRACTCONST = 55.0969;
const TIMECONST = 4.184;
//var gender = document.getElementById("gender").innerHTML;
var gender = "male";
var weight = document.getElementById("weight");
var age = document.getElementById("age");
var time = document.getElementById("time");
var hr = 140;//dummy number
function calculate(){
if (gender = "male"){
var calorieCount = ((age * AGECONST) - (weight * WEIGHTCONST) + (hr * HRCONST) - SUBTRACTCONST) * time / TIMECONST;
}
//else if (gender = "female"){
//}
var calorieCountOut = calorieCount.toString();
document.getElementById("output").innerHTML = calorieCountOut;
}