Pension Calculator

pension.js

var _ = require("underscore");

var percent = function (i) {
    return i / 100;
}

var pensionSumCalculator = function (params) {
    var default_params = {
            current_savings_in_pensions_funds: 0,

            gross_salary: 7500,
            employer_provision: 5, // percent
            worker_provision: 5, // percent
            severance_pay_provisions: true, // does the employer put to the fund severance pay provisions

            estimated_yield: 4, // percent

            yearly_management_fee: 1.25, // percent
            deposits_fee: 0, // percent

            age_years: 25,
            age_months: 2,
            pension_age: 67
        };

    p = _.extend({}, default_params, params);

    var months_until_pension =
            (p.pension_age * 12) - (p.age_years * 12) - p.age_months;

    var monthly_provision_percent =
            percent(p.employer_provision) +
            percent(p.worker_provision) +
            percent(p.severance_pay_provisions ? 100 / 12 : 0),
        monthly_provision = monthly_provision_percent * p.gross_salary,
        monthly_provision_after_deposits_fee = monthly_provision * (1 - percent(p.deposits_fee));

    var pension_sum = p.current_savings_in_pensions_funds;
    for (var i = 0; i < months_until_pension; i++) {
        pension_sum *= (
                1 +
                Math.pow(1 + percent(p.estimated_yield), 1/12) -
                Math.pow(1 + percent(p.yearly_management_fee), 1/12)
        );

        pension_sum += monthly_provision_after_deposits_fee;
    }

    return parseInt(pension_sum);
};

total_fees = function (params) {
    return pensionSumCalculator(_.extend({}, params, {deposits_fee: 0, yearly_management_fee: 0})) - pensionSumCalculator(params);
};

console.log(total_fees());