Write both the term and date
Net 30 is commonly used to mean payment within thirty days of the invoice date. Showing the actual due date removes the need for the customer to calculate it. Confirm the counting method in your agreement, especially where weekends or holidays matter.
Give usable payment instructions
State the currency and agreed payment method, and ask the customer to use the invoice number as a reference. Check account details carefully before sending. Never include passwords or payment-card credentials in an invoice.
An example for a project invoice
For an invoice issued on 1 September 2026, thirty calendar days gives a due date of 1 October 2026. A concise note could read: Please pay by 1 October 2026 and use INV-026 as the payment reference.
Do not invent penalties after the fact
A calculator can show interest arithmetic, but it does not authorize charging interest or fees. Confirm the agreement and applicable requirements before adding a charge. Send a courteous reminder and check whether payment is already in transit.