Sunday, June 20, 1948.
The basic idea was to substitute a much smaller number of deutsche marks (DM), the new legal currency, for reichsmarks. The money supply would thus contract substantially so that even at the controlled prices, now stated in deutsche marks, there would be fewer shortages. The currency reform was highly complex, with many people taking a substantial reduction in their net wealth. The net result was about a 93 percent contraction in the money supply.
What caused the so-called miracle? The two main factors were currency reform and the elimination of price controls, both of which happened over a period of weeks in 1948. A further factor was the reduction of marginal tax rates later in 1948 and in 1949.