Par swap rate
= Par swap rate
{title2=$s=(1-P_0(T))/\sum_{t=1}^TP_0(t)$}
The fixed rate making an <interest rate swap> have zero initial value. For unit accrual periods, unit notional and payments $r_t-s$, the floating-leg value is $1-P_0(T)$ and the fixed-leg annuity is $\sum_{t=1}^TP_0(t)$. The formula changes when accrual lengths or payment schedules differ.