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Mathematical calculation for years to reach savings goal
Old 08-29-2014, 02:12 PM   #1
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Mathematical calculation for years to reach savings goal

I googled and googled and couldn't' find a formula to solve for how long (Years) it takes to reach a savings goal. I wanted this for my retirement Excel spreadsheet. Given current principle, interest, annual contribution, and future value.

I found the FV formula...

FutureValue= Principal(1+Rate)^Years + Contribution [((1-Rate)^Years)-1]/Rate

So I broke out my pen, paper and did the algebra....

Years =Log Base [1+R] of [(C+R*FV)/(R*P+C)]

Just posting for anyone who might find it useful for their excel's.
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Old 08-29-2014, 08:43 PM   #2
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Why do algebra? Just use Solver in Excel. Or was it the "technical challenge"?
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Mathematical calculation for years to reach savings goal
Old 08-29-2014, 09:24 PM   #3
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Mathematical calculation for years to reach savings goal

I guess i dont know how to use solver.


But ya, i was a little proud to break out a logarithm after 15years
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Old 08-30-2014, 07:36 AM   #4
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Try the NPER function. NPER returns the number of periods for an investment based on periodic, constant payments and a constant interest rate. Input the pv (your current savings) and pmt (annual contributions) as negative numbers and fv (your savings goal) as a positive number and rate (your expected earnings rate per year) and it will return the number of years needed to reach your goal.

NPER(rate,pmt,pv,[fv],[type])
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