The Long-Run Determination of the Interest Rate The Long-Run Determination of the Interest Rate In the short run, an increase in the money supply from to pushes the interest rate down from r1 to r2 and the economy moves to E2, a short-run equilibrium. In the long run, however, the aggregate price level rises in proportion to the increase in the money supply, leading to an increase in money demand at any given interest rate in proportion to the increase in the aggregate price level, as shown by the shift from MD1 to MD2. The result is that the quantity of money demanded at any given interest rate rises by the same amount as the quantity of money supplied. The economy moves to long-run equilibrium at E3 and the interest rate returns to r1.