From a non-taxable standpoint, 0% is the lowest rate that may be charged to anyone (not just relatives).
From a taxable standpoint, the Applicable Federal Rate is the lowest rate that may be charged to anyone (not just relatives) if the lender wants to avoid paying taxes on the difference between the rate charged and the Applicable Federal Rate.
Effectively, any loan with a rate under the Applicable Federal Rate is giving someone a gift of the difference as interest. Since the borrower is receiving the benefit of the gift, the lender must pay the taxes associated with the gift.
A link to the current Applicable Federal Rate is included below as part of this answer.
Prime rate
The "Prime Interest Rate" is the interest rate used by banks to base all their loan interest rates (and sometimes other interest rates) on and is usually lower than the lowest rate charged on loans to customers with the best credit ratings.
The interest rate of the lowest bidder whose bid is accepted
The true annual rate of charged interest is called the annual percentage yield. It is the interest charged and compounded against.
The "prime" rate, which is regulated by the Federal Reserve Commission, with its' well-known chairman, Alan Greenspan. Prime is the interest rate that is charged to banks and lending institutions. It is THE basic rate which determines all other rates.
What the base line interest rates are when you are taking out your mortgage will determine which is the best value. Remember what is the lowest rate now may not be the lowest in a couple of years.
The Capital One Platinum Prestige card has the lowest interest rate with an intro APR of 0%. They also appear to have the lowest interest rate after the intro period ranging between 10.8% - 18.9%
Prime Rate -A+
The lowest interest rate varies day to day as of now (2009) you could probably get a 5-5.25% rate on a 30 year loan.
The average interest for the lowest refinancing mortgage rate depends on the company and how long one has been paying the loan and the value of what is left. An example is one to four percent interest rate.
Basic savings
prime rate