You would be much better off to have it and not be asked for it at the rental counter or should somebody hit you or something than you would be to not have it and need it.

The only place I've ever been asked to show it has been Italy when picking up rentals.

While it's good for a year, that assumes that your regular drivers license is also good for a year, if you regular license expires in a month, your international driving permit will need to be redone after you renew your license.