How can I predict missing values based on existing data?

Question

So I have a table of data and there are missing values from 79 to 85. How can I approximate the missing values based on the data before 79? (86.5 is peak value)

I tried Excel functions FORECAST and others, but it seemed none of them calculated those values properly.

Image of data here:

https://i.stack.imgur.com/2FVzK.png

Answer 1

There are plenty of reasonable ways of predicting values, and you should check which one of them adapts best to the nature of your data. For instance, if it seems to be converging over time, I would start with moving averages. But then again, predicting 5 values over 80 is prone to huge error.

Answer 2

It seems that your function in that specific region can be estimated with a low degree polynomial. I suggest you try regression for quadratic polynomial estimate or linear regression.