I personally like to keep my tax returns and back-up materials for 7 years. I keep one banker’s box in my attic. Inside the box there are 7 “box bottom” hanging file folders labeled:

2018
2017
2016
2015
2014
2013
2012

Inside each hanging folder are my tax returns and back up materials for that year.

When my accountant is done with my 2018 taxes, I will create a 2018 folder, put the folder and the papers into the attic box in front of 2017 and then shred 2012.

This is my SYSTEM. I hope you have one too!