Editing Fisher effect (section)

==Derivation==

The ''nominal'' interest rate is the accounting interest rate – the percentage by which the amount of dollars (or other currency) owed by a borrower to a lender grows over time, while the ''real'' interest rate is the percentage by which the real purchasing power of the loan grows over time. In other words, the real interest rate is the nominal interest rate adjusted for the effect of inflation on the purchasing power of the outstanding loan.

The relation between nominal and real interest rates, and inflation, is approximately given by the [[Fisher equation]]:

:<math>r = i - \pi^e</math>

The equation states that the [[real interest rate]] (<math>r</math>), is equal to the [[nominal interest rate]] (<math>i</math>) minus the expected [[inflation rate]] (<math>\pi^e</math>). 

The equation is an approximation; however, the difference with the correct value is small as long as the interest rate and the inflation rate is low. The discrepancy becomes large if either the nominal interest rate or the inflation rate is high. The accurate equation can be expressed using periodic compounding as:

:<math>1+i =(1+r)\times (1+\pi^e)</math>

If the real rate <math>r</math> is assumed to be constant, the nominal rate <math>i</math> must change point-for-point when <math>\pi^e</math> rises or falls. Thus, the Fisher effect states that there will be a one-for-one adjustment of the nominal interest rate to the expected inflation rate. 

The implication of the conjectured constant real rate is that monetary events such as [[monetary policy]] actions will have no effect on the real economy&mdash;for example, no effect on [[Real versus nominal value (economics)|real spending]] by consumers on [[consumer durables]] and by businesses [[fixed investment|on machinery and equipment]].