Using a fixed day sounds like a good way to have discipline. Usually the due date is some number of days (like 21) past the billing period date. The billing period end date is always some fixed day of the month, but the actual due date fluctuates due to the different lengths of months. If you pay a bit early and make it a fixed date, that could be a useful tool to stay in line. You can then program it into your smartphone calendar as a recurring item, too. Of course, in online banking you can also set up things to have the bill paid automatically; but there are downsides to these "set up and forget" schemes.