Invoice Due Date Calculator

How the due date is worked out

A due date is the answer to one question: N days after what? The calculator supports the three conventions that cover almost every invoice in circulation.

• Net N — the full amount is due N days after the invoice date. Net 30 is the most common term in the United States, followed by Net 15 and Net 45. The word net means no discount applies, so the whole balance is payable.
• End of month (EOM) — the balance is due on the last day of the invoice month, which gives a supplier a clean month-end receivables run. EOM + 15 pushes it to the 15th of the following month, and EOM + 30 to the end of the following month.
• Business days — counts working days rather than calendar days, starting from the next working day after the invoice date, skipping weekends and (optionally) the eleven US federal holidays.

The default is calendar days because that is what "Net 30" means by convention. If your agreement says "30 business days" it is reaching roughly six weeks into the future instead of one month, and the difference is worth catching before you sign.

Tying a deadline to the federal calendar? The 2027 federal holiday calendar lists every observed date, including the two that move.

Payment terms, and what they actually mean

The two-number notation is the one people misread. In 2/10 Net 30, the 2 is a percentage, the 10 is a day count, and Net 30 is the fallback deadline. It reads as "two percent off if you pay within ten days, net amount due in thirty."

Where the clock starts

This is the single biggest source of invoice disputes, and it is usually not written down.

• Invoice date. The clock starts the day the invoice is issued. Standard for services and for goods already delivered.
• Receipt of invoice. Some corporate buyers and public bodies start the clock when the invoice reaches their accounts payable department, which can be days later — and their terms often say so explicitly.
• Delivery or acceptance. For goods, the clock may start when the buyer accepts delivery, not when the seller ships.

Under the Uniform Commercial Code, payment for goods is due at the time and place the buyer receives them unless the contract says otherwise. That default is far stricter than Net 30 — so if you intend to offer terms, put them in writing on the invoice.

Weekends and holidays

A Net 30 invoice dated Friday 18 September 2026 falls due on Sunday 18 October. The deadline itself does not move unless your contract says it should, but payments are made on the next business day, so the money usually arrives Monday 19 October. Switch to the business-days mode to see the date the cash actually moves, and keep both numbers when chasing a late payment.

If a holiday lands inside the window, business-days mode excludes it. That matters most around late November and late December, when two federal holidays can sit inside a single 30-day window.

Late fees and statutory interest

A late fee is only collectible if the agreement provides for one, or if a statute does. Two useful landmarks:

• Federal Prompt Payment Act. Federal agencies must pay a proper invoice within 30 days and owe interest automatically on anything later. If you invoice the federal government, that clock and rate are set by statute rather than by your terms.
• State prompt payment acts. Most states have equivalents for public construction and some for private construction, with their own interest rates and notice requirements. Private-sector late fees are contractual, and a rate that looks punitive may not be enforceable.

Three worked examples

1. Net 30 issued on a Friday

An invoice dated Friday 18 September 2026 with Net 30 terms is due Sunday 18 October 2026. Calendar-day terms mean the deadline lands on a weekend. The effective payment date is usually the next business day, Monday 19 October.

If the client's terms instead say 30 business days, forward 30 working days from 18 September lands on Friday 30 October — twelve calendar days later. The two readings differ by almost a fortnight on a single invoice, which is why the term has to be written down.

2. The 2/10 Net 30 decision

A $25,000 invoice with 2/10 Net 30 terms offers $500 off for paying on day 10 instead of day 30. Twenty days of earlier payment buys a $500 saving, which is an annualised rate of roughly 37.2%.

Put the other way: if your business can borrow at anything under about 37%, taking the discount and using the credit line is the better trade. Declining a 2/10 Net 30 discount is one of the most expensive decisions a small business can make by default, because it happens silently on every invoice.

3. EOM + 15 across a month end

An invoice dated 12 October 2026 with EOM + 15 terms is due on the last day of October plus 15 days — Sunday 15 November 2026. The administrative appeal of EOM terms is that every invoice issued in October falls on the same November date, which turns 30 payment runs into one.

The cost is real though. An invoice issued on 1 October waits 45 days; one issued on 31 October waits only 15. Suppliers who accept EOM terms are effectively lending the buyer an average of about 15 extra days.

Five mistakes to avoid

1. Leaving "Net 30" off the invoice. Under the UCC default, payment for goods is due on delivery. If you intend to offer 30 days, say so on the document — an unstated term cannot be enforced later.
2. Counting the invoice date as day one. Net 30 runs from the date printed, so the span is 30 days and the due date is day 30, not day 31. The calculator excludes the start day, which matches how banks and payroll systems count.
3. Assuming calendar days when the contract says business days. Thirty business days is about six weeks. On a large invoice that difference is worth thousands of days of float.
4. Forgetting the discount deadline on 2/10 Net 30. The discount window closes on day 10 whether or not you have received the invoice internally. If a buyer's slow intake process eats the window, the discount is gone.
5. Charging a late fee that was never agreed. Without a contractual clause or a statutory right, a late fee is not collectible, and states cap the rates that are. Put the clause in the original agreement, not just on the invoice.

Sources and standards

FAQ

How do I calculate an invoice due date?

Enter the invoice date and the payment terms. For Net 30 the due date is the invoice date plus 30 calendar days. For EOM it is the last day of the invoice month, and EOM + 15 adds fifteen days to that.

Are Net 30 terms calendar days or business days?

By long-standing convention Net 30 means 30 calendar days, which is why the calculator defaults to calendar mode. Some agreements specify business days instead — the calculator supports both, with an optional US federal holiday exclusion.

What does Net 30 actually stand for?

"Net" means the full amount is payable with no discount. So Net 30 means the entire balance is due 30 days after the invoice date. In the two-number form 2/10 Net 30, the discount applies only inside the first ten days and the net amount is due at thirty.

What does EOM + 15 mean on an invoice?

EOM means the invoice is due at the end of the invoice month. EOM + 15 means fifteen days after the end of that month, so an October invoice under EOM + 15 is payable on 15 November.

What if the due date falls on a weekend?

The deadline itself stays on the weekend day unless the contract moves it, but payments are made on the following business day. Switch to business-days mode to see when the money actually moves, and quote both dates when chasing a payment.

Does the 30 days start from the invoice date or the day it is received?

That depends entirely on what the contract says, and it is the most common dispute in accounts payable. Net terms normally run from the invoice date; some corporate buyers and most public bodies run from receipt of a valid invoice. Write it down.

Is there a default payment term if we did not agree one?

Under the Uniform Commercial Code, payment for goods is due at the time and place the buyer receives them unless the contract provides otherwise. That is far shorter than Net 30, so relying on a default is a poor substitute for stating terms.

How do I calculate a discount like 2/10 Net 30?

The first number is the percentage discount, the second is the number of days to claim it, and the net term is the fallback deadline. Take 2% off the balance if paid within ten days; otherwise the full amount is due at thirty days.

What is the annualised value of a 2/10 Net 30 discount?

About 37.2%. Paying 20 days early saves 2%, and annualising that over the 20-day window produces the equivalent rate. If your borrowing cost is below that, taking the discount and using credit is the better trade.

Can I charge interest on an overdue invoice?

Only if the agreement provides for it or a statute applies. Federal agencies owe interest automatically under the Prompt Payment Act, and many states have prompt payment acts with their own rates. In the private sector an interest clause has to be in the original agreement to be enforceable.

How do I handle a list of invoices at once?

Use the bulk due date tool — paste your invoice list, get every due date, and export back to CSV. It is the same arithmetic applied a few hundred rows at a time.

Are the dates calculated in my time zone?

No. All arithmetic runs on calendar dates with no clock time attached, so no result can shift by a day because of a time zone or a daylight saving change.