What it means
The option is based on a reference interest rate, such as a short-term benchmark rate, and a notional amount, which is the sum used to calculate the payment but never actually exchanged. The strike rate is the level above which the option pays out.
If the rate at expiry is above the strike, the buyer receives a cash payment, and if not, the option expires worthless. Companies mostly use these options to protect themselves against rising rates.
A business with a floating-rate loan pays more when rates go up, so buying an interest rate call option provides a payment that offsets the extra cost. If rates stay low, the company simply loses the premium and still enjoys its cheaper loan.
This is the key difference from a forward or a swap, which lock in a rate and remove the chance of benefit if rates fall. With an option, the buyer's loss is capped at the premium while the possible gain is large.
The price of that flexibility is the premium paid up front. The size of the premium depends on the strike, the time to expiry and how much rates are expected to move.
A strike close to current rates costs more than a distant strike, and a longer option costs more than a shorter one. Higher expected volatility, meaning bigger swings in rates, also raises the price.
Investors and banks also use these options for speculation or to manage portfolios. A bond trader who expects rates to rise can buy such an option and benefit without owning the underlying bonds.
The seller of the option takes on the risk of paying out and earns the premium in exchange. The terminology can be confusing, because options on bond prices and options on rates move in opposite directions.
A call on a rate gains when the rate rises, which is the same direction as a put on a bond price, so always check what the underlying is.
In practice
Real-world examples.
Example
A property developer has a $20,000,000 floating-rate loan and fears higher rates. She buys a call option on the reference rate with a strike close to the current level, so any rise is partly offset by the option's payout. The premium is paid at the start and is treated as a cost of protection, whether or not the option is ever used.
Example
A fund manager expects central banks to raise rates faster than the market believes. He buys interest rate call options with a distant strike, paying a small premium for a chance of a large gain.
Example
A bank sells an option to a corporate client and earns the premium. It then hedges its own risk in the market so it is not exposed to a rise in rates. The bank selling the option usually offers several strikes, and the buyer chooses by comparing the premium with how much protection each one provides.
Formula
Calculation
Payoff = Notional x Maximum of (Reference rate - Strike rate, 0) x Days / 360
Net profit = Payoff - Premium paid
A company buys an option on a notional $10,000,000 with a strike rate of 4% covering a 90-day period, and pays a premium of $18,000. At expiry the reference rate is 5%. The rate is 1 percentage point above the strike, so payoff = 10,000,000 x 0.01 x 90 / 360 = 100,000 x 0.25 = $25,000.
Net profit = 25,000 - 18,000 = $7,000. If the rate had finished at or below 4%, the payoff would have been $0 and the loss would be the premium of $18,000.Case study
Seen in the real world.
Stonebridge Logistics is an illustrative, fictional haulage company with a $15 million floating-rate loan. The finance director worried that rates might rise sharply and push interest costs above the company's covenant limit.
She bought an interest rate call option with a strike of 4.5% on the full amount for one year, paying a premium of $60,000. Rates did rise to 6.5% by the end of the term, so the extra interest on the loan was 15,000,000 x 0.02 = $300,000.
The option payoff also equalled about 15,000,000 x 0.02 = $300,000, which offset the higher cost, leaving only the premium of $60,000 as the net cost of protection. In this illustrative story, the director explained to the board that the premium was like an insurance cost, paid whether or not the protection was used. At the board meeting the director also explained that the option had a cost even in a good year, because the premium was gone if rates stayed low. She added that the company had considered a swap instead, but chose the option because it wanted to keep the benefit if rates fell.
Watch out
Common mistakes.
- Believing the option commits the buyer to anything, when the buyer can let it expire and lose only the premium.
- Forgetting that the notional amount is only a calculation base and is not paid or received.
- Ignoring the premium when judging the hedge, which can turn an apparent gain into a loss.
Questions
People also ask.
When does an interest rate call option pay out?
It pays when the reference rate at expiry is above the strike rate.
How is it different from an interest rate swap?
A swap locks in a rate and removes both gains and losses, while an option protects against a rise but keeps the benefit if rates fall.
Who sells these options and why?
Banks and other institutions sell them to earn the premium, and they manage their own risk by hedging in the market.
From the founder's library
Take it further with the book.
Build your financial confidence beyond this definition. Shihan's full-length guide, Accounting Fundamentals, takes the same plain-English approach and turns it into a complete, practical playbook for non-finance managers, business owners and students - with chapter-end quiz answers and presentation slides included.
25% off with code MMHQ25, applied at checkout. Priced in USD - checkout may show the equivalent in your local currency.
View the book and save 25%Related