We have discovered quite a number of exoplanets to date. The Kepler spacecraft has examined 150,000 stars and found 1,059 exoplanets.
We know that Kepler, as well as all other exoplanet searches to date, can only find planets that cross in front of their star. That means that a large percentage of existing planets will not be detected. In addition, a lot of planets may be too small for the sensitivity of our detectors.
From these facts, has anyone calculated the probability of a star having a planetary system? I am guessing it is likely quite close to 1, i.e. all stars have planets, but I have not seen anyone figures for it.