Why does this function return undefined, if base case isn't met in first iteration?

"use strict";

let moves = 0;

function Mormons(startingNumber, reach, target) {
  if (startingNumber >= target) return moves;
  startingNumber += startingNumber * reach;
  moves++;
  //console.log(startingNumber, moves);
  Mormons(startingNumber, reach, target);
}

console.log(Mormons(40, 2, 121));

This case should return 2 and if you remove the comment, it prints 2 on the second iteration, also it returns 0 if target is less than or equal to startingNumber, but with any other case it returns undefined. I'm new to JavaScript btw.