miniRetirement.php

<?php

class MiniRetirement {

    private $workedYears = 0;
    private $retirementYears = 0;
    private $totalYears = 0;
    private $unaccountedYears = 0;

    public function __construct($totalYears) {
        $this->unaccountedYears = $this->totalYears = $totalYears;
        return $this;
    }

    public function addWorkYear($monthlyIncome, $monthlySpend, $retirementMonthlySpend=null) {
        $retirementMonthlySpend = $retirementMonthlySpend ?? $monthlySpend;
        $this->workedYears++;
        $this->unaccountedYears--; 
        $amountSavedInAYear = floatval(($monthlyIncome-$monthlySpend)*12);
        $numberOfRetirements = floatval($amountSavedInAYear/($retirementMonthlySpend*12));
        $this->retirementYears += $numberOfRetirements;
        $this->unaccountedYears -= $numberOfRetirements;
        return $this;
    }

    public function print() {
        echo "Worked Years: ".$this->workedYears.'<br>';
        echo "Retirement Years: ".$this->retirementYears.'<br>';
        echo "Unaccounted Years: ".$this->unaccountedYears.'<br>';
        return $this;
    }

   
}

(new MiniRetirement(18))
->addWorkYear(10000, 2000)
->addWorkYear(10000, 1500)
->addWorkYear(10000, 1500)
->addWorkYear(10000, 2000)
->addWorkYear(10000, 1500)
->addWorkYear(10000, 1500)

->print();

?>