DEFINITION of 'Cost Of Savings Index - COSI Index'

A popular index used for certain adjustable-rate mortgages (ARMs). The index is a weighted average of the rates of interest on the deposit accounts (sometimes called cost of savings) of the federally insured depository institution subsidiaries of Golden West Financial Corporation (GDW). These subsidiaries currently operate under the name World Savings.

GDW computes the COSI on the last day of each calendar month and announces it on or near the last business day prior to the fifteenth day of the following calendar month.

BREAKING DOWN 'Cost Of Savings Index - COSI Index'

The COSI index is a stable index. Historically, it is not as volatile as some other popular mortgage indexes, such as the one-month LIBOR index. It also tends to lag other mortgage indexes when it comes to adjusting to changes in interest rates.

RELATED TERMS
  1. Current Index Value

    The most recently published value of an underlying interest rate ...
  2. Mortgage Index

    The benchmark interest rate an adjustable-rate mortgage's fully ...
  3. ARM Index

    The benchmark interest rate to which an adjustable rate mortgage ...
  4. Discretionary ARM

    An adjustable-rate mortgage on which the lender has the right ...
  5. Interest Rate Index

    An index that is based on the interest rate of a financial instrument ...
  6. Fully Indexed Interest Rate

    The interest rate on an adjustable-rate loan that is calculated ...
Related Articles
  1. Insights

    How Interest Rates Affect the Housing Market

    Understand how rate changes can affect home prices and learn how you can keep up.
  2. Investing

    Tales From The Trenches: Don't Count On Luck

    ChartAdvisor experts illustrate why it's important to stick to your strategy.
  3. Personal Finance

    Adjustable-Rate Mortgage Indexes: Know Your Benchmark

    Understanding these benchmarks can help you select the most competitive adjustable-rate loan.
  4. Personal Finance

    ARMed And Dangerous

    In a climate of rising interest rates, having an adjustable-rate mortgage can be risky.
  5. Personal Finance

    Shopping for a Mortgage in 2017? Use This Tool First

    As home-buying technology has progressed, the process of finding the best mortgages rates for 2017 can all be done online.
  6. Personal Finance

    This ARM Has Teeth

    Find out how to avoid getting bitten when your mortgage rate resets.
  7. Personal Finance

    Millennials Guide: How to Pick the Right Mortgage

    Here’s help in finding the perfect, affordable loan for that home you have been dreaming about.
  8. Investing

    Subprime Is Often Subpar

    Proceed with caution when considering these short-term, high-interest mortgages.
  9. Personal Finance

    5 Things You Shouldn't Tell Your Mortgage Broker

    Applying for a mortgage can be a strenuous process. Here are five things to avoid doing when meeting with your mortgage broker.
  10. Personal Finance

    5 Reasons To Save For A Big Mortgage Down Payment

    You may be anxious to buy a home, but taking time to save a large down payment has numerous advantages.
RELATED FAQS
  1. How does a point change in a major index effect its equivalent exchange-traded fund?

    The S&P 500 and Dow Jones Industrial Index (DJIA) are two of the most well-known indexes tracking the movement of the U.S. ... Read Answer >>
Trading Center