I have some capital losses from 2011 that were not reported on my 2011 return. These were overlooked and did not affect 2011 or 2012 as I had enough carryover to meet the max amount.

For 2013 I am under the max, and I found out that I had these losses from 2011. Even though it would not affect my previous year's return, do I need to amend my 2011 return, or can I just report them on my 2013 return?

Any help is appreciated.

You cannot carryover any losses to any year until they have been claimed on a return for the year when the losses happened. you can't carry over what you forgot for the previous year, you need to amend that return ; you should file your current with the amount you are eligible to claim . If you do not do the 1040X, then you can never claim them, on your 2011 return or any other year