The best fit values for the SM parameters imply that the potential for the Higgs boson developes a Planck-scale vacuum with negative energy, which may result in decay of the current vacuum state. In this talk we will go through the standard discussion of vacuum (in)stability during inflation and then show the significance of backreaction from classical gravity. After discussing inflationary vacuum stability, we will concentrate on the non-perturbative effects during reheating and show that they may also induce vacuum decay for large inflationary scales. In particular, we conclude that inflation and reheating constrain the non-minimal coupling between the SM Higgs and gravity to be close to 1/6. arXiv:1407.3141 and arXiv:1506.04065.