Hello and thanks in advance for any help.

I’m trying to translate an arima model into an excel spreadsheet for calculations for something I’m studying.

The model is a 4,1,0 model that I used the Arima function in R to fit.

The coefficients are
ar1:.2499
ar2:-.0060
ar3:-.1258
ar4:-.0046

the xreg coefficient is -29.5243.

No matter what I try, I cant seem to get the formula right so any help would be greatly appreciated.

Thank you so much!

I think I’m getting hung up with which variables I need to difference and which errors to use as inputs as I forecast forward.