bill.js

/*
  add your bills to the bills array.
  repeat: once | weekly | bi-weeky | monthly | bi-monthly
    if using bi-monthly, you'll need a first and second argument
    see examples below
*/
var bills = [
  {"name": "Some Bill",       "amount": -672,     "next": new Date("2020-09-25"), repeat: "monthly"},
  {"name": "Income",          "amount": 2000.00,  "next": new Date("2020-09-25"), repeat: "weekly"},
  {"name": "Loan",            "amount": -291.70,  "next": new Date("2020-09-28"), repeat: "bi-monthly", first: 9, second: 28},
  {"name": "More Income",     "amount": 1049.50,  "next": new Date("2020-10-02"), repeat: "bi-weekly"}
];

// put your current balance here
const current = 748.09;
// put today's date here. The String is important so that it does the time right.
const today = new Date("2020-09-23");
// this is how far out your want to project.
const projection = new Date("2020-10-01");
var projectedBalance = current;

bills.sort((a, b) => (a.day > b.day) ? 1: -1);
console.log("Projected Balance: of " + projectedBalance + " on " + today.toISOString().slice(0, 19).replace(/-/g, "/").replace("T", " "));
for (var d = today; d < projection; d.setDate(d.getDate() + 1)) {
  
  const billsFound = bills.filter(bill => (bill.next.getMonth() === d.getMonth() && bill.next.getDate() === d.getDate()));
  if (billsFound.length > 0) {
    
    for (var i = 0; i < billsFound.length; i++) {
  
      const bill = billsFound[i];
      
      console.log(bill.name + " bill found on " + d.toISOString().slice(0, 19).replace(/-/g, "/").replace("T", " ") + " for $" + bill.amount);
      projectedBalance += bill.amount;
      console.log("Projected Balance: of $" + projectedBalance + " on " + d.toISOString().slice(0, 19).replace(/-/g, "/").replace("T", " "));
      const repeat = bill.repeat;
      
      switch(repeat) {
        case "once":
          break;
        case "monthly":
          bill.next = new Date(bill.next.setMonth(bill.next.getMonth() + 1));
         break;
        case "weekly":
          bill.next = new Date(bill.next.setDate(bill.next.getDate() + 7));
          break;
        case "bi-weekly":
          bill.next = new Date(bill.next.setDate(bill.next.getDate() + 14));
          break;
        case "bi-monthly":
          if (bill.first == d.getDate()+1) {
            bill.next = new Date(bill.next.setDate(bill.second));
          } else if (bill.second == d.getDate()+1) {
            const year = d.getFullYear();
            var first = bill.first.toString();
            var month = (bill.next.getMonth() + 1).toString();
            if (year === 11) year = 0;
            if (month.length == 1) month = "0" + month;
            if (first.length == 1) first = "0" + first; 
            bill.next = new Date(year.toString() + "-" + month + "-" + first);
          }
          break;
        default:
          break;
      }
    }
  }
}

console.log("Projected Balance: of " + projectedBalance);