Hi Frank,
First off - which D4D, 2.0 or 2.2? If 2.0 then 1CD or 1AD engine (2006 is about the changeover)?
These will make a difference as will whether you have had your car serviced, tyre condition & inflation, load in/on car, the type of journey & driver that you are & the ambient temperature.
To give you an idea I typically average 42mpg winter - 45mpg summer over the year in mixed motoring. However, I have seen it range from under 30 to middle 60s depending upon the individual journey.
Also, remember that the car range counts down to "reserve" (afaik ~9 litres in an Avensis) & not empty. So when the car initially says range 0 you may in fact have enough fuel for another ~90 miles. It's typical Toyota caution.