Calculating an inflation rate

[dtwiddy]

I'm wondering if there is a way to use a formula to calculate the inflation rate needed here instead of using Goal Seek every time.

As an example, I will make a payment in month one of $1,500. I want to increase my payment each month, compoundedly, so that I have a total amount at the end of the year of $25,000. I can use Goal Seek to find out that I would have to increase each payment by 5.7922% but would really like to have it update the interest rate if I changed the initial payment OR the ending balance. I'm not sure if this is possible because the formula would have to work forward and backward. I want to specify the initial payment and the ending balance, then ask for the necessary increase of payments throughout the year. Any suggestions?

Book1 (version 1).xlsb
	R	S	T
13	Payment	Cumulative	Inflation
14	$1,500	$1,500	5.7922%
15	$1,587	$3,087
16	$1,679	$4,766
17	$1,776	$6,542
18	$1,879	$8,421
19	$1,988	$10,408
20	$2,103	$12,511
21	$2,225	$14,736
22	$2,354	$17,089
23	$2,490	$19,579
24	$2,634	$22,213
25	$2,787	$25,000
Sheet1

Cell Formulas
Range	Formula
S14	S14	=R14
R15	R15	=S14*($T$14+1)
S15:S25	S15	=S14+R15
R16:R25	R16	=R15*($T$14+1)

 

[joeu2004]

Book1
	R	S	T
13	Pmt	Bal	%Chng
14	$1,500.00000000000	$1,500.00000000000	5.79218414830017%
15	$1,586.88276222450	$3,086.88276222450
16	$1,678.79793403018	$4,765.68069625468
17	$1,776.03700184706	$6,541.71769810174
18	$1,878.90833553600	$8,420.62603363774
19	$1,987.73816630800	$10,408.36419994570
20	$2,102.87162128661	$12,511.23582123230
21	$2,224.67381799387	$14,735.90963922620
22	$2,353.53102223110	$17,089.44066145730
23	$2,489.85187302609	$19,579.29253448340
24	$2,634.06867853167	$22,213.36121301510
25	$2,786.63878698492	$25,000.00000000000
Sheet1

Formulas:
R15: =R14*(1+$T$14)
S14: =R14
S15: =S14+R15
T14: =RATE(12, -1500, 0, 25000)