The NPER (number of periods) function will do this for you. E.g.,

=NPER(Rate,Payment,PresVal,FutureVal,Type)

where Rate is the annual interest rate = 0.04, Payment is annual
withdrawl = -50,000, FutureVal ending value = 0, Type indicates
whether withdraw is at end or begining of period (0 or 1).

In your example, you'll exhaust the principle in 37.38 years.

Cordially,
Chip Pearson
Microsoft MVP 1998 - 2010
Pearson Software Consulting, LLC
www.cpearson.com
[email on web site]





On Sun, 20 Dec 2009 14:44:01 -0800, ridgerunner
wrote:

I am not very good with financial worksheet functions and hope that someone
here can help. Is there a function that will return how long funds will last
if you earn a static interest rate and withdraw a static amount of money that
is more than the interest earned? Let's say, for example, the amount of
money is $1,000,000, the interest rate is 4% and the yearly withdrawal is
$50,000?