There's an art and a science to telling your customers exactly when to pay you. The more clear and specific you are about your due dates, the the more likely they are to be observed.
Although it's common to use the word "net" in invoicing--as in "Net 15"--using the word "days" instead can eliminate confusion for some less business-savvy customers. By stating the terms in days, "Due in 15 days" you'll make the deadline clear for everyone.
Don't Make Recipients Do Math
Yes, it's a relatively easy task to look at an invoice date of November 27th and terms of Net 15 and figure out that the invoice is due December 12th. But your goal is to remove as many obstacles as possible and make it super simple for a customer to process your invoice correctly. So the best practice is to include both the payment terms and the due date on the invoice.
“Payment is due 15 days from the date of this invoice. Please pay by December 12, 2016”
Don't Allow Accounting Systems to Do Math Wrong
Many accounting systems default to using the date the invoice is entered into the payment system as the invoice date. If the payment date is stored in their system, that means they may incorrectly calculate the due date if it's not staring them in the face. Giving the specific due date helps to eliminate the problem.
Clients have a funny way of looking at time. Give them definite and clear dates to work with and you're more likely to get paid on time.
Looking for information on optimal terms? Check our our blog post, "Everything you Know About Payment Terms Is Wrong". Spoiler alert: The answer is between 14 and 21 days.