Invoice due date calculator
Terms are a date
"Net 30" means thirty days from the invoice date, and an invoice issued on 7 September 2026 on those terms is due on 7 October 2026. Print the date, not the phrase. An accounts department reading "30 days" starts counting from whenever the invoice reached them, or was approved, or was entered, and each of those is later than the date you meant. The date on the sheet leaves nothing to count from and nothing to argue about.
Counting the days
Terms count calendar days, not working days, unless your terms say otherwise, and a due date that lands on a Saturday is still the due date: the bank transfer can be sent on a Saturday even if it settles on Monday. Where a customer's system pays on a run, the last Friday of the month say, you can either accept that the money arrives on the run after your date or set the date to fall before the run. Ask a new commercial customer when their runs are; it is the single most useful thing to know about them.
Which terms to set
Thirty days is what large companies expect and what small ones cannot afford. For domestic work, due on completion or seven days is normal, and a customer who has just watched the job finish is at the most willing they will ever be. For a small commercial job, fourteen days. Save thirty for the customers who genuinely cannot pay faster and who are worth the wait. The guide to payment terms sets out what each does to your bank balance over a year.
The day after
The day after the due date is when the invoice is late, and when the first reminder should go. Not a stern one: the customer who meant to pay simply forgot, and a friendly line with the invoice attached collects most of them. The ones who did not mean to pay need to know you noticed, and the reminders get firmer from there. Chasing a late invoice has the wording for each stage. The calculator's "as of today" line is the number to put in that first message.