List the dates
Set out the next 8 to 12 weeks. Put regular outgoings such as payroll and rent alongside tax, suppliers and any one-off costs. Use the dates cash actually leaves the account.
Allow for late payments
List the invoices you expect to collect, using a conservative date for customers that sometimes pay late. Work out the lowest projected balance and rerun the figures with a delay in your largest receipts.
Consider the full picture
Before borrowing, see whether changing supplier terms or invoice collection timing reduces the gap. If you still need funding, allow for repayments in the same schedule.