  We study the impact of the precision determination of oscillation parameters
in the JUNO experiment on half-life predictions for neutrinoless double beta
decay. We show that the solar neutrino mixing angle can be measured by JUNO
with below 1% uncertainty. This implies in particular that the minimal value of
the effective mass in the inverted mass ordering will be known essentially
without uncertainty. We demonstrate that this reduces the range of half-life
predictions in order to test this value by a factor of two. The remaining
uncertainty is caused by nuclear matrix elements. This has important
consequences for future double beta decay experiments that aim at ruling out
the inverted mass ordering or the Majorana nature of neutrinos.
