Calculate how much you save after some years for monthly saving...

MonthlySavingInterestCalculator.rb

@year = 40 #total years you want to save monthly
@months = @year*12
@saving = 200 #amount of money you want to save monthly
@yearly_interest_rate = 6 #yearly interest rate for monthly saving
@interest_calculation_duration_in_month = 3		#interest is calculated each 3 months
@monthly_interest_rate = (@yearly_interest_rate/100.0)/12.0
@amount = 0
(1..@year).each do |y|
	(1..12).each do |m|
		@amount = @amount + @saving
		if(m % @interest_calculation_duration_in_month == 0)
			@interest = 0
			(1..@interest_calculation_duration_in_month).each do |im|
				@interest = @interest + @saving*im*@monthly_interest_rate
			end
			@interest = @interest + ((@amount-(3*@saving))*3*@monthly_interest_rate)
			@interest = @interest - (@interest*5.00/100.0) #5% income tax

			 @amount = @amount + @interest
		end
	end

end

 print @amount