Polynomials have a fundamentally different shape than s-shaped curves, since
polynomials are unbounded and s-shaped curves are not. If you are fitting a
broad enough range that you need a 6+ degree polynomial, you might do better
fitting a function that is actually s-shaped. Without knowing what kind of
data you have, the best I can suggest is that a 4- or 5-parameter logistic
(Google it) is used frequently in biochemistry. Any cumulative probability
distribution function is also s-shaped.

"Vikram" wrote:

Hi,

I have data which generates an s-shaped curve. The best trendlines that can
be obtained in Excel are of the order 6 and that isn't close to the accuracy
I am seeking.

Does anyone know if there is a way in Excel to get a trend line of order
higher than 6?

Thanks in advance,
Vikram