Swaption
Quantitative Finance glossary · Derivatives Pricing & Volatility Surfaces
Definition
Option to enter an interest-rate swap at a future date — payer swaption gives the right to pay fixed (call on rates), receiver swaption the right to receive fixed (put on rates). European swaption price under the annuity measure follows Black's formula with the par swap rate as the underlying: V = A(0),[S_0,N(d_1) - K,N(d_2)], where A(0) = sum_i τ_i,P(0,T_i) is the annuity. Bermudan/American extensions priced by tree or LSM Monte Carlo. The dominant rates-volatility instrument — swaption-vol matrix is the analogue of the equity vol surface.
Swaption in plain English
First, a "swap" is a deal where two parties trade payment streams — classically one pays a fixed interest rate while the other pays a floating (changing) one, a common way to hedge against rates rising or falling. A swaption is simply an *option* on that deal: the right, but not the duty, to enter such a swap at a future date, so you lock in flexibility without committing. A "payer" swaption lets you choose to pay fixed (you win if rates shoot up), and a "receiver" lets you receive fixed (you win if rates drop) — like reserving a fixed-price contract you'll only sign if the market moves your way. Swaptions are the main tool for trading how *volatile* interest rates might be, and the grid of their prices is the rates world's version of the stock market's "volatility surface."
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