A month can balance on paper while cash runs short during a particular week. A cash flow calendar shows the timing behind the totals.
Put each expected payment and each expected income date into one calendar. Start with the balance you can actually use, then calculate a running balance after each event. Use a separate line for a payment that may arrive late or cost more than expected.
Review the weeks where the running balance falls. Mark any due dates you need to confirm and recheck the calendar when the timing changes. The example worksheets below show how to organise a week-by-week view.
Further reading: CFPB Your Money, Your Goals worksheets.