class FinancialCalculator::Fv

Calculate the future value of a series of equal of payments

Attributes

num_periods[R]

@return [Numeric] The number of periodic payments

payment[R]

@return [Numeric] The amount of the periodic payment

present_value[R]

@return [Numeric] The current value

rate[R]

@return [Numeric] The discount rate used in the calculation

result[R]

@return [Numeric] The result of the future value calculation

Public Class Methods

new(rate, num_periods, payment, present_value = 0, pay_at_beginning = false) click to toggle source

Create a new future value calculation

@see en.wikipedia.org/wiki/Future_value @example

FinancialCalculator::Fv.new(0.02, 10, -100) #=> FV(1094.972100)

@param [Numeric] rate The discount (interest) rate to use @param [Numeric] num_periods The number of periodic payments @param [Numeric] payment The amount of the periodic payment @param [Numeric] present_value The current value @param [Boolean] pay_at_beginning Whether the payments are made at the beginning or end of each period @return [FinancialCalculator::Fv] A Fv object @raise [ArgumentError] Raises an ArgumentError if num_periods is less than 0 or a required numeric

field is given a non-numeric value
# File lib/financial_calculator/fv.rb, line 34
def initialize(rate, num_periods, payment, present_value = 0, pay_at_beginning = false)
  validate_numerics(rate: rate, num_periods: num_periods, payment: payment, present_value: present_value)

  if num_periods < 0
    raise ArgumentError.new('Cannot calculate future value with negative periods. Use present value instead.')
  end

  @rate             = Flt::DecNum(rate.to_s)
  @num_periods      = Flt::DecNum(num_periods.to_s)
  @payment          = Flt::DecNum(payment.to_s)
  @present_value    = Flt::DecNum(present_value.to_s)
  @pay_at_beginning = pay_at_beginning
  @result           = solve(@rate, @num_periods, @payment, @present_value, pay_at_beginning)
end

Public Instance Methods

inspect() click to toggle source
# File lib/financial_calculator/fv.rb, line 49
def inspect
  "FV(#{result})"
end
pays_at_beginning?() click to toggle source

@return [Boolean] Whether the payments are made at the beginning of each period

# File lib/financial_calculator/fv.rb, line 54
def pays_at_beginning?
  @pay_at_beginning
end

Private Instance Methods

solve(rate, num_periods, payment, future_value, pay_at_beginning) click to toggle source
# File lib/financial_calculator/fv.rb, line 60
def solve(rate, num_periods, payment, future_value, pay_at_beginning)
  annuity_due = pay_at_beginning ? 1 : 0
  compound = (1 + rate) ** num_periods

  -((present_value * compound) + (payment * (1 + rate * annuity_due) * (compound - 1) / rate))
end