0% interest balance transfer

Quick question, hopefully simple.

I did a promotional 0 interest balance transfer for 12 months a while back. If there is a balance after the 12 months, do I owe all the equivalent of deferred interest? Or does that balance, at the end of term, now have monthly interest?

Ive done promotional store cards before, and balance is due by date or you pay all the interest that was deferred.

But, I don't know about navy fed and a balance transfer. Nor do I believe anywhere it actually states a deffered interest. Can't find an actual answer on the site, or statements.