On Aug 10, 8:03 am, bonjella wrote:
I have a starting balance, the annual interest rate of my savings
account, and how much I can save each month. I also have a target
ammount in mind.

From this I want to know how many Months I will have to save this
before my Target is met.

Suppose your savings APY is 3%, you have $25,000 already, you plan to
save $750 per month, and your goal is $50,000. Then
the number of months is:

=roundup(nper(3%/12, -750, -25000, 50000), 0)

if I want to buy a home in 2 years
time, how much I'll have saved by then

=rounddown(fv(3%/12, 24, -750, -25000), 0)

And you might want to know how much you would have to save each month
in order to meet your goal:

=roundup(-pmt(3%/12, 24, -25000, 50000), 0)

my answers are coming out negitive

First, some people would say that the negative results are not
necessarily wrong. But like you, I like my results to be positive.

In this case, the key is to think of the "present value" (starting
balance) and "payments" (monthly amount saved) as outflows (negative)
and the "future value" (goal) as an inflow (positive). Then adjust
the sign of the result to be positive as you choose. In this case,
only the result of the PMT function needs to be changed.


Notes:

1. Computing the monthly interest rate as 3%/12 is an estimate.
First, since I am talking about the APY, the monthly rate should be
computed by (1+3%)^(1/12)-1. But the difference in this case is small
-- only $1 per month. Second, interest in some (not all) savings
accounts compound daily. But again, the difference is small. On the
other hand, many savings accounts compute simple interest based on a
daily balance or average daily balance; in that case, compounding is
indeed on a monthly basis.

2. I choose between ROUNDUP and ROUNDDOWN in to yield the more
conservator answer, depending on what is computed. Again, the
difference is not large enough to really make much of a difference.

3. You might want to use the after-tax interest rate. That is the APY
times 1-t, where "t" is sum of the applicable federal and state tax
rates.