Caps, Floors and Collars

A company with a floating-rate loan wants protection if rates spike, but doesn't want to give up the benefit if rates fall — and doesn't necessarily want to pay a large upfront premium either. Interest-rate options built specifically for this job come in three related shapes: a cap, a floor, and a collar that combines them.

The mechanics, one reset at a time

A cap isn't one option; it's a series of them, one per reset date over the life of the loan, each called a "caplet." Each caplet pays the difference between the floating rate at that reset and the cap's strike, if positive, applied to the notional for that period:

$$\text{Caplet payoff} = \max(r - K, 0) \times \text{Notional} \times \tau$$

In words: if the floating rate $r$ resets above the strike $K$, the caplet pays the excess, scaled by the notional and the length of that period $\tau$; if the rate resets below the strike, the caplet pays nothing. A floorlet is the same formula flipped, paying $\max(K - r, 0)$.

Drag the strikes on the explorer above to see how buying a cap and selling a floor narrows the range of outcomes: above the cap strike, the borrower is protected; below the floor strike, they've given up the benefit of even-lower rates in exchange for that protection being cheaper (or free).

Worked example

A company has a $50 million floating-rate loan resetting quarterly, currently referencing a rate of 4.80%. It buys a 5.50% cap and, to offset the cost, sells a 3.50% floor — a zero-cost collar, meaning the cap premium and floor premium happen to be equal.

If the rate resets at 6.00% next quarter: the cap pays $\max(6.00\% - 5.50\%, 0) \times 50{,}000{,}000 \times 0.25 = 62{,}500$, offsetting the extra interest cost above 5.50%. If the rate instead resets at 2.50%: the sold floor obligates the company to pay $\max(3.50\% - 2.50\%, 0) \times 50{,}000{,}000 \times 0.25 = 125{,}000$, meaning the company doesn't get to benefit from rates below 3.50% — it effectively pays as if the rate were 3.50%.

What this means in practice

Caps are pure insurance: pay a premium, get protection, keep all the upside. Collars are cheaper insurance financed by giving up some of the upside. Treasurers, mortgage originators, and structured-product desks all use these building blocks constantly — a mortgage borrower's rate cap and a corporate treasurer's hedged floating loan are priced with exactly the same caplet math.