// Periods to retirement
// rate: interest rate per period on savings
// payment: amount invested per period
// target: desired dividend per period
// returns: minimum periods until period return on savings is greater than target
function PTR(rate, payment, target, period) {
  var periods = 0;
  var savings = 0;

  if(!period) {
    period = 1;
  }

  while(savings * rate < target) {
    periods += period;
    savings += rate * savings + payment;
  }
  return periods;
}

// Savings at retirement
// rate: interest rate per period on savings
// payment: amount invested per period
// target: desired dividend per period
// returns: minimum savings for dividend to be greater than target
function SAR(rate, payment, target) {
  var savings = 0;
  while(savings * rate < target) {
    savings += rate * savings + payment;
  }
  return savings;
}

// Periods to accrue
// rate: interest rate per period on savings
// payment: amount invested per period
// target: desired dividend per period
// returns: minimum number of periods before target return per period is met
function PTA(rate, payment, target) {
  var periods = 0;
  var savings = 0;
  while(savings < target) {
    periods++;
    savings += rate * savings + payment;
  }
  return periods;
}

// Federal tax
// gross: gross income
// status: "single"/"married"/"separate"
// allowances: number of allowances you have
function FT(gross, status, allowances) {
  var tax_rates = {
    "single" : [[0, 9225, .1], [9225, 37450, .15], [37450, 90750, .25], [90750, 189300, .28], [189300, 411500, .33]],
    "married" : [[0, 18450, .1], [18450, 74900, .15], [74900, 151200, .25], [151200, 230450, .28], [230450, 441500, .33]],
    "separate" : [[0, 9225, .1], [9225, 37450, .15], [37450, 75600, .25], [75600, 115225, .28], [115225, 205750, .33]]
  }[status];

  gross = gross - allowances * 4050 - tax_rates[0][1];

  var total_tax = 0;
  for(i in tax_rates) {
    if(gross > tax_rates[i][0]) {
      if(gross <= tax_rates[i][1]) {
        total_tax += tax_rates[i][2] * (gross - tax_rates[i][0]);
      } else {
        total_tax += tax_rates[i][2] * (tax_rates[i][1] - tax_rates[i][0]);
      }
    } else {
      break;
    }
  }

  return total_tax ;
}