The occurrence of planets orbiting ultracool dwarfs is poorly constrained .
We present results from a Guest Observer program on NASA ’ s K2 spacecraft to search for transiting planets orbiting a sample of 827 ultracool dwarfs .
Having found no transiting planets in our sample , we determined an upper limit on the occurrence of planets .
We simulated planets orbiting our sample for a range of orbital periods and sizes .
For the simulated planets that transit their host , we injected the transit light curve into the real K2 light curves , then attempted to recover the injected planets .
For a given occurrence rate , we calculated the probability of seeing no planets , and use the results to place an upper limit on planet occurrence as a function of planet radius and orbital period .
We find that short period , mini-Neptune- and Jupiter-sized planets are rare around ultracool dwarfs , consistent with results for early- and mid-type M dwarf stars .
We constrain the occurrence rate \eta for planets between 0.5 and 10 R _ { \Earth } with orbital periods between 1 and 26.3 days .