<prompt> Human: A few months ago I signed up for a Capital One Quicksilver card for some international travel no foreign transaction fee. I set up my account to auto-pay the entire card balance every month.Checking my account today, I saw that my auto-pay applied for April as usual covering the entire balance, but I was still charged interest on the full April statement balance.I called into their support since I assumed this was a mistake, and after some digging the rep found the issue: during April I had applied some rewards points to my account balance about 100 worth. This meant the auto-pay amount was 100 less than the full statement balance. The way Capital Ones system works is that if your payment amount does not exactly match or exceed the statement balance, you are charged interest on the entire statement balance.The rep stated that this is working as intended and that any time you use rewards points auto-pay in this way, you will be charged interest for the statement balance that month. The only way to fix that interest charge is to call into customer support the rep did remove the interest from my account.I believe you can avoid this problem if you dont use the statement credit option when redeeming rewards points, but cant confirm that myself now.Overall I found this behavior on Capital Ones part to be exceptionally surprising and misleading. Ive used a Chase Freedom card for years and their system works as one would expect in this situation. I will likely stop using the QuickSilver card outside of international travel with extra vigilance in the future.TL;DR: Capital One will still charge you interest if you apply rewards points to your statement balance when using auto-pay.edit: formatting  <response>: Hmm doesnt work like that for me. I have it setup to redeem as a statement credit whenever it reaches the 25 minimum, Ive never paid interest on the account. 