Hi all

First of all, thanks for taking the time out to read this.

I'm in a bit of a precarious situation. I have access to recent data but cannot retrieve earlier data. Thing is, this is for a important report and there cannot be any missing data so I figure why not forecast the figures but of course backwards. I've tried to reverse engineer forecasting but ended running into negative figures which doesn't make sense since I'm looking at total healthcare expenditure figures.

Would appreciate if anyone could shed light on appropriate methods to backward prediction in excel or R.

Thank you.