More realistically, there is no way we will increase our spending by the inflation factor. We are "sticky upward" on spending and I have the historic figures to prove it. Although the official inflation figures used in these studies are real, real people don't see their cost of living increase that much. If prices for food, petrol, rent, travel etc increase, we hold firm and spend less. By just holding to 1 point under inflation on the increases, 4% becomes quite safe and closer to 5% reasonable.