It's not quite like that.  You can buy back anything you sold for a loss any time you want to.  But if you don't wait 31 days, you fall victim of the arcane and obtuse "wash sale rules".  Actually, the "wash sale rules" aren't all that complicated, but calculating them for oneself is.  That's why there are services such as Gainskeeper that do all the arithmetic for you, then present you with the results / outcomes .   ( this is not an endorsement of Gainskeeper or any other such service )