Understanding credit card minimum payments

climbintheladderouttadebt

I'm curious about calculations for the minimum payments on my credit card, I'm sorry if I'm asking something obvious or repeated!

Basically, upon going over my statements since 2007 when the account was opened, my minimum payments each month are calculated by adding that months interest plus the ppi due - is that normally how it's worked out? I thought it was a % of what your balance was...

So looking at my statements, my balance never really went down much, even though min payments were approx £13 and I paid £20.

Am I just being thick or is this a bit suss?

Thank you for any clarity put on this!