Invoice Due Date Calculation: Examples for Net 7, 15, and 30

Short answer

To calculate an invoice due date, start with the date your payment terms use as the reference point, then add the agreed number of calendar days. For example, an invoice dated August 8 with Net 15 terms is normally due August 23. If your contract uses business days, month-end rules, or a different trigger, follow that agreement instead.

Write both the payment term and the exact due date on the invoice. The invoice payment terms guide explains why clear wording reduces payment delays.

Common invoice due date examples

Assume the invoice date is August 8, 2026:

• Due on receipt: payment is expected when the customer receives the invoice.
• Net 7: payment is due August 15, 2026.
• Net 15: payment is due August 23, 2026.
• Net 30: payment is due September 7, 2026.
• Net 45: payment is due September 22, 2026.

These examples use calendar days. If weekends or public holidays change the contractual due date, state the rule clearly and apply it consistently.

What date should the calculation use?

The starting date may be the invoice date, the date the invoice is received, the date goods are delivered, or the date a milestone is approved. The correct trigger should come from your contract or purchase order.

For digital invoices, using the invoice date is simple, but it may not match the customer’s accounts-payable process. If the customer requires a receipt confirmation, save that confirmation with the invoice record.

Net terms versus a fixed due date

Net terms describe the number of days allowed for payment. A fixed due date states the exact date. Both can be clear:

• Payment due within 15 days of the invoice date.
• Payment due August 23, 2026. Terms: Net 15.

Showing the exact date is usually better because the customer does not need to calculate it. A simple invoice created with the free invoice generator can include both the term and the due date.

Month-end and business-day rules

Some businesses use terms such as 30 days end of month or payment due on the last business day. These rules can produce a different date from ordinary Net 30 terms.

Do not replace a month-end rule with a standard day count. Put the exact resulting date on the invoice and explain any unusual rule in the payment notes. If your customer uses a purchase order, compare the invoice with the purchase order before sending.

Avoid these due date mistakes

Common errors include:

• Calculating from the wrong date
• Using Net 30 but entering a 30th-of-the-month date
• Forgetting that the invoice month has fewer than 30 days
• Copying yesterday’s due date into a new invoice
• Showing a due date that conflicts with the contract
• Including a payment term but no exact date

Before sending, compare the date, term, and customer agreement. The small business invoice checklist provides a broader pre-send review.

What happens after the due date?

Record the invoice as overdue when the agreed date passes without full payment. Send a factual reminder with the invoice number, amount, due date, and payment instructions. Use the invoice payment reminder templates for suitable wording.

If late charges were agreed, apply them only according to the contract and applicable law. Keep the original invoice and any later adjustment in your records.

FAQ

Does Net 30 mean 30 calendar days?

Often it means payment is due 30 calendar days after the agreed starting date, but contracts can define business days or month-end rules differently. Check the agreement.

Is the invoice due date the same as the payment date?

The due date is the deadline stated by the seller. The payment date may be when the customer sends funds or when the funds clear, depending on the agreement and payment method.

Can I change the due date after sending an invoice?

Only with a clear agreement and an updated record. Tell the customer in writing, preserve the original invoice, and document the revised terms.