  In the cold dark matter paradigm, structures form hierarchically, implying
that large structures contain smaller substructures. These subhalos will
enhance signatures of dark matter annihilation such as gamma rays. In the
literature, typical estimates of this boost factor assume a concentration-mass
relation for field halos, to calculate the luminosity of subhalos. However,
since subhalos accreted in the gravitational potential of their host loose mass
through tidal stripping and dynamical friction, they have a quite
characteristic density profile, different from that of the field halos of the
same mass. In this work, we quantify the effect of tidal stripping on the boost
factor, by developing a semi-analytic model that combines mass-accretion
history of both the host and subhalos as well as subhalo accretion rates. We
find that when subhalo luminosities are treated consistently, the boost factor
increases by a factor 2-5, compared to the typical calculation assuming a
field-halo concentration. This holds for host halos ranging from sub-galaxy to
cluster masses and is independent of the subhalo mass function or specific
concentration-mass relation. The results are particularly relevant for indirect
dark matter searches in the extragalactic gamma-ray sky.
