calc_credit_profit.js

function calc({
  balance, 
  months, 
  percent, 
  cashbackPercent, 
  earnings, 
  spendings
}){
  let totalIncome = 0;
  let credit = 0;
  for(let i = 0; i < months; i++) {
    let income = Math.round(balance * percent/100 /12);
    let cashback = Math.round(spendings * cashbackPercent / 100);
    balance += income + cashback;
    console.log("Balance: ", balance, ", Income: ", income, ", cashback: ", cashback);
    balance += earnings - credit;
    credit = spendings;
    totalIncome += income + cashback;
  }
  console.log("Total Income: ", totalIncome);
}

calc({
  balance: 10000, 
  months: 12, 
  percent: 10, 
  cashbackPercent: 1, 
  earnings: 10000, 
  spendings: 5000
});