How to implement a Gompertz curve in Excel?

[rfeu]

Hi guys,

Background
I would like to model a new product launch in Excel using the Gompertz curve (or maybe other sigmoid functions if easier):

I would like the user to enter only three inputs if possible
1) Final market share reached by a product at time t. E.g., 10%
2) Time t. E.g., April 2018
3) Date of product launch. E.g., October 2016

In other words, the user knows that a product will be launched in October 2016 and that in April 2018, this product will reach a maximum market share of 10%.
I would like to model at the month level (October 2016, November 2016...until April 2018), the evolution of the market share.

Question
I have worked with linear function/regression in Excel, but never modeled something like a GOmpertz.
Any idea where to start would be more than welcome (I have looked at the following thread but do not really understand how to implement it for my question: http://www.excelforum.com/excel-prog...cal-curve.html)

Thank you!

[MrShorty]

Are you doing a regression like in the other thread, or do you already know the desired values for a, b, and c, and need to calculate the curve for those values? Is there a specific part of the other sigmoidal problem that you have trouble implementing? It seems to me that, assuming you are doing a regression, it should be the same steps as I outlined in post 8 of that thread, and that the spreadsheet that shg uploaded in post 13 should provide a good example of how this sort of spreadsheet can be set up.

If you look at my post 8, Step 2 (post 8) is the only step that is equation specific, and you should just need to replace the sigmoidal equation given there with your equation for the Gompetz curve. The other steps are generic regression steps.
If you look at shg's spreadsheet in post #13, the same basic spreadsheet should work, simply replacing the formulas in D11:D20 with your equation for the Gompetz curve.

Which part of this do you need help with?

[rfeu]

Thank you for your answer.
After more research on the Internet, I found the answer to my question here: http://www.clear-lines.com/blog/post...ion-curve.aspx
Might be helpful for those trying to solve the same issue.