Context : Gamma-ray binaries are thought to be composed of a young pulsar in orbit around a massive O or Be star , with their gamma-ray emission powered by pulsar spindown .
The number of such systems in our Galaxy is not known .

Aims : We aim to estimate the total number of gamma-ray binaries in our Galaxy and to evaluate the prospects for new detections in the GeV and TeV energy range , taking into account that their gamma-ray emission is modulated on the orbital period .

Methods : We model the population of gamma-ray binaries and evaluate the fraction of detected systems in surveys with the Fermi -LAT ( GeV ) , HESS , HAWC and CTA ( TeV ) using observation-based and synthetic template lightcurves .

Results : The detected fraction depends more on the orbit-average flux than on the lightcurve shape .
Our best estimate for the number of gamma-ray binaries is 101 _ { -52 } ^ { +89 } systems .
A handful of discoveries are expected by pursuing the Fermi -LAT survey .
Discoveries in TeV surveys are less likely .
However , this depends on the relative amounts of power emitted in GeV and TeV domains .
There could be as many as \approx 200 HESS J0632+057-like systems with a high ratio of TeV to GeV emission compared to other gamma-ray binaries .
Statistics allow for as many as three discoveries in five years of HAWC observations and five discoveries in the first two years of the CTA Galactic Plane survey .

Conclusions : Continued Fermi -LAT observations are favoured over ground-based TeV surveys to find new gamma-ray binaries .
Gamma-ray observations are most sensitive to short orbital period systems with a high spindown pulsar power .
Radio pulsar surveys ( SKA ) are likely to be more efficient in detecting long orbital period systems , providing a complementary probe into the gamma-ray binary population .