It feels great to send out invoices. But you can’t pay bills or make payroll with great feelings.

Invoices aren’t real money, as every entrepreneur understands. Just because someone owes you, it doesn’t mean you have money in the bank.

Crimps in cash flow have killed many “profitable” businesses. Until your customers pay up, you can’t use that money to pay creditors, suppliers and other debts, such as business loans.

And debts like loans cost you more money the longer you owe them. If your cash flow prevents you from retiring interest-charging debts early, late invoice payments cost you money, not just time.

Simply keeping on top of your billing goes a long way to keeping your cash flow flowing, and your bank account in the black.

Some tips:

1. Adopt a firm billing cycle, whether it’s monthly, weekly or immediately. Make sure invoices go out promptly.

2. Include clear and complete payment terms on all invoices so there’s no misunderstanding of when and how much the customer is to pay.

3. Track invoices. As soon as payments become late, send a courtesy note or make a phone call. Be polite. Be flexible. Maybe installments or extensions can mutually be agreed upon.

4. When payments are unreasonably late according to your contractual terms, make a firm but business-like demand for payment. State clearly that unless full payment is received by a definite date, appropriate legal or collection measures will be taken.

5. For persistently delinquent debts, go to court or turn the collection over to an agency. This is a last resort, but preferable to a loss.