Question

Decision #2: Planning for Retirement

Erich and Mallory are 22, newly married, and ready to embark on the journey of life.   They both plan to retire 45 years from today. Because their budget seems tight right now, they had been thinking that they would wait at least 10 years and then start investing $3000 per year to prepare for retirement. Mallory just told Erich, though, that she had heard that they would actually have more money the day they retire if they put $3000 per year away for the next 10 years - and then simply let that money sit for the next 35 years without any additional payments – then they would have MORE when they retired than if they waited 10 years to start investing for retirement and then made yearly payments for 35 years (as they originally planned to do).   Please help Erich and Mallory make an informed decision:   

Assume that all payments are made at the END a year (or month), and that the rate of return on all yearly investments will be 7.2% annually.  

(Please do NOT ROUND when entering “Rates” for any of the questions below)

1. How much money will Erich and Mallory have in 45 years if they do nothing for the next 10 years, then put $3000 per year away for the remaining 35 years?

2. How much money will Erich and Mallory have in 10 years if they put $3000 per year away for the next 10 years?

b2) How much will the amount you just computed grow to if it remains invested for the remaining 35 years, but without any additional yearly deposits being made?

3. How much money will Erich and Mallory have in 45 years if they put $3000 per year away for each of the next 45 years?
4. How much money will Erich and Mallory have in 45 years if they put away $250 per MONTH at the end of each month for the next 45 years? (Remember to adjust 7.2% annual rate to a Rate per month!)
5. If Erich and Mallory wait 25 years (after the kids are raised!) before they put anything away for retirement, how much will they have to put away at the end of each year for 20 years in order to have $1,000,000 saved up on the first day of their retirement 45 years from today?

Answer 1

a)	Future value of annuity			=	P[{(1+r)^n}-1]/r
		where
			P	=	3000
			r	=	7.2% or 0.072
			n	=	45-10 = 35 years
	Money after 45 years			=	3000*[{(1+0.072)^35}-1]/0.072
				=	3000*[11.3977-1]/0.072
				=	3000*10.3977/0.072
				=	$       433,237.50
b)	Future value of annuity			=	P[{(1+r)^n}-1]/r
		where
			P	=	3000
			r	=	7.2% or 0.072
			n	=	10 years
	Money after 10 years			=	3000*[{(1+0.072)^10}-1]/0.072
				=	3000*[2.004-1]/0.072
				=	3000*1.004/0.072
				=	$         41,833.33
b2)	Future value			=	Amount*(1+r)^n
		where
			amount	=	$41,833.33
			n	=	35 years
			r	=	0.072
	Future value			=	41833.33*(1+0.072)^35
				=	41833.33*11.3977
				=	$       476,803.75
c)	Future value of annuity			=	P[{(1+r)^n}-1]/r
		where
			P	=	3000
			r	=	7.2% or 0.072
			n	=	45 years
	Money after 45 years			=	3000*[{(1+0.072)^45}-1]/0.072
				=	3000*[22.8436-1]/0.072
				=	3000*21.8436/0.072
				=	$910,150
d)	Future value of annuity			=	P[{(1+r)^n}-1]/r
		where
			P	=	250
			r	=	7.2% /12 =0.6% or 0.006
			n	=	45 years*12 months=540
	Money after 45 years			=	250*[{(1+0.006)^540}-1]/0.072
				=	250*[25.2877-1]/0.006
				=	250*24.2877/0.006
				=	$   1,011,987.50
e)	Future value of annuity			=	P[{(1+r)^n}-1]/r
		where
			P	=	?
			r	=	7.2% or 0.072
			n	=	20 years
		$1,000,000		=	P*[{(1+0.072)^20}-1]/0.072
		$1,000,000		=	P*[4.0169-1]/0.072
		$1,000,000		=	P*3.0169/0.072
		$1,000,000		=	=P*41.902
		1000000/41.902		=	P
		$23,865		=	P
	They need to put $ 23,865 for 20 years to accumulate $1,000,000 at their retirement.
Note-	In requirement (d) the monthly rate can also be taken as [(1.072)^1/12]-1 = 0.005811 or 0.5811% considering 7.2% as effective annual rate
	There may be slight difference in answer due to decimal places.Please do not downvote on that basis
	Please upvote the answer
	If you have doubt,feel free to ask in comments