In an
interest rate swap, the arbitrary amount over which
interest is calculated. Suppose the two
legs of the swap are a
fixed interest rate, say 3.5%, and a
floating interest rate, say
LIBOR + 0.5%, and the notional principal amount is $1 million. In such a swap, the only things traded are the two interest rates, which are calculated over the notional principal amount. That is, the $1 million is never exchanged, but the interest is calculated with reference to it. For example, the fixed interest is 3.5% of $1 million (or $35,000). It is also called the
notional value.