A possible source of free energy available for accelerating charged particles is conversion of magnetic energy to particle energy in reconnecting magnetic fields. Recent simulations using test particles suggests that reconnection may efficiently accelerate particles to th maximum energies that are observed in several astrophysical contexts. A simple analytic formula is used in conjunction with the simulation results to predict the maximum energy achievable in a particular plasma environment with the result that in solar flares reconnection is capable in accelerating particles to several GeV. In magnetospheric substorms the predicted maximum can reach several hunderd keV, and near magnetic sector crossings in the solar wind the maximum energy can approach 100 keV.