  The fate of massive stars with initial masses >8M$_\odot$ depends largely on
the mass-loss rate (\mdot ) in the end stages of their lives. Red supergiants
(RSGs) are the direct progenitors to Type II-P core collapse supernovae (SN),
but there is uncertainty regarding the scale and impact of any mass-loss during
this phase. Here we used near and mid-IR photometry and the radiative transfer
code DUSTY to determine luminosity and \mdot\ values for the RSGs in two
Galactic clusters (NGC 7419 and $\chi$ Per) where the RSGs are all of similar
initial mass ($M_{\rm initial}$$\sim$16M$_\odot$), allowing us to study how
\mdot\ changes with time along an evolutionary sequence. We find a clear, tight
correlation between luminosity and \mdot\ suggesting the scatter seen in
studies of field stars is caused by stars of similar luminosity being of
different initial masses. From our results we estimate how much mass a
16M$_\odot$ star would lose during the RSG phase, finding a star of this mass
would lose a total of 0.61$^{+0.92}_{-0.31}$M$_\odot$. This is much less than
expected for \mdot\ prescriptions currently used in evolutionary models.
