 True interest rate

 
The real interest rate is larger than the "nominal rate" if it is compounded more frequently than the period for which the nominal rate is quoted. This calc finds the true rate of interest in such cases.
 
Usually the nominal rate will be given per year, and the compounding will be monthly (i.e. 12 rest periods), but other possibilities exist. For continuous compounding, set the number of rest periods to a large number (e.g. 10,000).  