  We discuss the production of primordial gravitational waves (GW) from
radiative inflaton decay during the period of reheating, assuming perturbative
decay of the inflaton either into a pair of bosons or fermions, leading to
successful reheating satisfying constraint from Big Bang nucleosynthesis.
Assuming that the inflaton $\phi$ oscillates in a general monomial potential
$V(\phi)\propto \phi^n$, which results in a time-dependent inflaton decay
width, we show that the resulting stochastic GW background can have optimistic
detection prospects, especially in detectors that search for a high-frequency
GW spectrum, depending on the choice of $n$ that determines the shape of the
potential during reheating. We also discuss how this GW energy density may
affect the measurement of $\Delta N_{\text{eff}}$ for bosonic and fermionic
reheating scenarios.
