Historically, inflation is in the U.S. causes prices to rise an average of 3-4% a year. Though is may sound insignificant, the reality is very different. Over 20 years at 4% annual inflation your expenses will double. When you are retired and relying on various sources of income be sure to factor in the inflation rate. Here is a 20 year table beginning with $50,000 of expenses in year one. The table is based on 4% annual inflation.