Rebasing changes the reference year (or base year) for the real (chained dollar and quantity index) estimates and price indexes and expresses GDP and other NIPA aggregates in terms of the prices of one year. The effect of rebasing is to produce chained-dollar estimates that are closer to additive for periods near the new base year. It is important to note that percentage changes based upon chain-type indexes are not affected by rebasing.
Generally, the year selected as the reference year is the latest year that will not be revised until the next comprehensive update. For the 2018 comprehensive update, real estimates were rebased from chained (2005) dollars to chained (2012) dollars.