Interest from the previous month
Is is possible to fund the interest category from October, when I get paid on November 3?
No; your income is only available going forward, not backward. However, it's relatively simple to budget for interest retroactively. You do it by budgeting directly to the CC payment category. If your income and fees category is overspent by $30 in October because you recorded interest that you couldn't afford to budget for, in November, your un-budgeted-for credit card debt will have gone up by $30. Budget $30 to that card's payment category to bring things square again.