You have five years after expiration to renew it without having to start over from scratch.
I just sent my renewal in the other day after my passport was expired for 15 months.
I have no plans to travel outside the US, I just started to feel naked without a passport after having one for so long.
Been more than 5 now. Plus, we have the gold star on our d’s if we want to fly in the states. Which we don’t want to do anymore.