achieved will be significantly higher than the APR initially calculated. This is especially problematic for mortgage loans, where typical loan repayment periods are 15 or 30 years but where many borrowers move or refinance before the loan period runs out, which increases the borrower's effective cost for any points or other origination fees. In theory, this factor should not affect any individual consumer's ability to compare the APR of the same product (same repayment period and origination fees) across vendors. APR may not, however, be particularly helpful when attempting to compare different products, or similar products with different terms. Interest-only loans Since the principal loan balance is not paid down during the interest-only term, assuming there are no set up costs, the APR will be the same as the interest rate. Three lenders with identical information may still calculate different APRs. The calculations can be quite complex and are poorly understood even by most financial professionals. Most users depend on software packages to calculate APR and are therefore dependent on the assumptions in that particular software package. While differences between software packages will not result in large variations, there are several acceptable methods of calculating APR, each of which returns a slightly different result. See also Compound interest References External links Convert an Effective Interest Rate to a nominal Annual Percentage Rate Convert a nominal Annual Percentage Rate to an Effective Interest Rate FDIC Finance Charge and APR calculation rules White Paper: More than Math, The Lost Art of Interest calculation Introduction to percentages and understanding APR with BBC raw money Mortgage Disclosure Improvement Act or MDIA How to Calculate Annual Percentage Rate (APR) by Self Banking Personal finance Interest rates Mathematical finance