An interest rate on a loan or security that fluctuates over time since it is based on an underlying benchmark interest rate or index that changes on a regular basis is referred to as having a variable interest rate. This type of interest rate is also referred to as a "adjustable" or "floating" rate at times.

What Is a Variable Interest Rate?

The borrower's interest payments will naturally decrease if the underlying interest rate or index goes down, which is one of the most obvious benefits of having a variable interest rate. On the other hand, if the underlying index goes up, then interest payments will go up as well. Fixed interest rates, on the other hand, do not change as frequently as variable interest rates.

The underlying benchmark interest rate or index for a variable interest rate differs depending on the type of loan or security, but it is usually linked to the LIBOR or the federal funds rate.  Variable interest rates can be observed in mortgages, credit cards, corporate bonds, derivatives, and various other securities or loan products.

Understanding Variable Interest Rates

When it comes to interest rates, a variable interest rate is one that shifts up and down in tandem with the rest of the market or with an index. Whether the London Inter-Bank Offered Rate (LIBOR) or the federal funds rate is used as the underlying benchmark interest rate or index for a loan or security with a variable interest rate is determined by the nature of the loan or security. However, these two rates are frequently used as the basis for such rates.

The prime interest rate in a country is one example of a benchmark rate that can be used to determine variable interest rates for mortgages, auto loans, and credit card debt. Banks and other financial institutions will charge customers an additional spread on top of this benchmark rate. The amount of this additional spread will vary depending on a number of factors, including the kind of asset being purchased and the customer's credit rating. As a result, a variable rate could advertise itself as "the LIBOR plus 200 basis points," which is equivalent to "plus 2%."

Mortgages on residential properties, for instance, can be obtained with interest rates that are fixed, meaning that they are unchangeable for the duration of the mortgage agreement, or with interest rates that are floating or adjustable, meaning that they are variable and change periodically in accordance with the market. Other types of securities, such as credit cards, corporate bond issues, swap contracts, and other types of investments, may also have variable interest rates.

The London Interbank Offered Rate (LIBOR) is being phased out because recent scandals and questions surrounding its validity as a benchmark rate. The Secured Overnight Financing Rate will take the place of the London Interbank Offered Rate (LIBOR) as of the 30th of June in 2023, as stated by the Federal Reserve and the regulators in the United Kingdom (SOFR). Following the conclusion of this phase-out process on December 31, 2021, the LIBOR one-week and two-month USD LIBOR rates will no longer be published.

Variable-Interest-Rate Credit Cards

Credit cards with variable interest rates have an annual percentage rate (APR) that is linked to a specific index, such as the prime interest rate. The most common time that the prime rate shifts is whenever the Federal Reserve makes a change to the federal funds rate, which then causes a shift in the rate that is associated with the credit card. Credit cards with variable interest rates have rates that can change at any time, even if the cardholder isn't notified in advance.

Customers who use credit cards with variable interest rates may not be informed if the card's interest rate changes.

Within the "terms and conditions" document that is associated with the credit card, the interest rate is most generally shared as the prime rate plus a particular percentage, with the particular percentage being tied to the creditworthiness of the cardholder. This is the most common way that the interest rate is expressed. The prime rate plus 11.9% is an illustration of one possible format.

Variable-Interest-Rate Loans and Mortgages

With the exception of the repayment schedule, loans with variable interest rates operate in a manner analogous to credit cards. The vast majority of loans are structured as instalment loans, which require a predetermined number of payments to be made before the loan is fully paid off by a predetermined date. A credit card is an example of a rotating line of credit. The minimum payment that must be made on a loan is subject to fluctuation based on the current interest rate as well as the number of payments that must be made before the loan is paid off.

An adjustable-rate mortgage is the term most commonly used to refer to a situation in which the interest rate on a mortgage loan is subject to change (ARM). The interest rate on many adjustable-rate mortgages (ARMs) remains stable for the first few years of the loan and only changes after that initial period has passed. Three, five, or seven years is a common choice for the fixed-interest-rate period on an adjustable-rate mortgage, which is expressed as a 3/1, 5/1, or 7/1 ARM, respectively. When the interest rate adjusts, there is typically a "cap" that is placed on the increase or decrease in rate that can take place as a result of the adjustment. You can get a rough estimate of the current interest rates on adjustable-rate mortgages by using a calculator that is available online.

Rates on adjustable-rate mortgages (ARMs) typically fluctuate according to a major mortgage index as well as a predetermined margin. Examples of major mortgage indices include the LIBOR, the 11th District Cost of Funds Index (COFI), and the Monthly Treasury Average Index (MTA Index). For instance, if a person obtains an adjustable-rate mortgage (ARM) with a 2% margin based on the LIBOR and the LIBOR is at 3% when the mortgage's rate adjusts, the rate will reset to 5%. (the margin plus the index).

Variable-Interest-Rate Bonds and Securities

In the case of bonds with variable interest rates, the LIBOR may serve as the benchmark rate. Some variable-rate bonds also use the yield on a United States Treasury bond with a maturity of five years, ten years, or thirty years as the benchmark interest rate. These bonds offer a coupon rate that is determined by a certain spread above the yield on U.S. Treasuries.

Fixed-income derivatives can also carry variable rates. One type of forward contract is known as an interest rate swap. This type of swap involves the exchanging of one stream of future interest payments for another stream of future interest payments based on a particular principal amount. To reduce or increase exposure to fluctuations in interest rates—or to acquire a marginally lower interest rate than would have been possible without the swap—interest rate swaps typically entail the exchange of a fixed interest rate for a floating interest rate, or vice versa. This can be done to reduce or increase the amount of exposure to fluctuations in interest rates. A swap also can involve the exchange of one type of floating rate for another, which is referred to as a basis swap. This type of swap is known as a basis swap.