For me it’s simple, and I don’t understand why so many in ‘our industry’ have such a problem.

Back in pre-historic times, you used to allow 30 (, 60 or 90) days so the client had time to pass the invoice to their accounts, the accounts raise a cheque and snail-mail it back to you. You then had to bank it and wait on clearance! In this day and age, who still uses cheques? A bank wire can be setup and money transferred AND received all in one day! No need for 30 days anymore.

And the simplest way of getting paid on time is to write into your contract that no website goes live or artwork released for print until the final invoice has been paid in full. I haven’t had anyone find this a problem, including a couple of bigger companies who you’d expect to be the dinosaurs with late payment.