Payment Due Date Calculator

"Net 30" is a phrase, not a date. Pick the invoice date and the term below and this works out the day payment is actually due — counting calendar days or business days, and moving the result off a weekend if that is how your terms work.

What this tool does

Payment terms are the single most common source of "I thought it was due next week" disputes, and almost all of them come from three ambiguities: whether the clock starts on the invoice date or the delivery date, whether the count is calendar days or business days, and what happens when the due date lands on a Saturday.

This calculator makes all three explicit. It shows the raw computed date and the adjusted date separately, so you can see exactly why the answer moved — which is also what you need if a customer ever queries it. Nothing here is a legal position on when payment becomes enforceable; that depends on your contract and your jurisdiction.

How it works

  1. Start from the invoice date

    The clock conventionally starts on the date the invoice is issued. Some contracts start it on delivery, or on receipt of a valid invoice — if yours does, enter that date instead. The calculator counts from whatever date you give it.

  2. Count the term

    Calendar days are the default: Net 30 from 15 January is 14 February. Business days is a different calculation, not a variation on the same one — Net 30 in business days is about six weeks, because weekends and holidays are skipped rather than counted.

  3. Adjust for non-working days

    If the computed date is a weekend or a public holiday, most terms move it to the next business day; some move it to the previous one. Both are offered, and the raw date stays visible so the shift is explainable.

  4. Carry it into the invoice

    The invoice date, due date and the terms label transfer straight into the generator, so the document says the same thing the calculation did.

Worked example

A design studio issues an invoice on Friday 1 January 2026 on Net 30 terms, with weekend adjustment.

Inputs

Invoice date
Thursday 1 January 2026
Payment term
Net 30 (calendar days)
Weekend rule
Move to next business day

Result

Raw due date
Saturday 31 January 2026
Adjusted due date
Monday 2 February 2026
Days from invoice
32

Why it matters: The term said 30 days; the customer actually has 32. That gap is invisible unless the calculation shows both dates — and it is exactly the gap that makes an aging report disagree with a customer’s own record.

Best practices

  • Write the due date on the invoice as a date, not as "Net 30". A date cannot be misread; a term can.
  • State which day the clock starts from in your terms — issue, delivery, or receipt of a valid invoice. Most disputes are about the start, not the length.
  • Pick one convention for weekends and apply it to every customer. Ad-hoc adjustment is what makes an aging report untrustworthy.
  • If you invoice internationally, remember public holidays are not shared. A due date that is a working day for you may not be for the payer’s bank.
  • Shorter terms get paid sooner far more reliably than late fees get paid at all. Net 14 with a clear date beats Net 30 with a penalty clause.

Common mistakes

Treating "Net 30" and "30 business days" as roughly the same

They differ by about two weeks. Net 30 in business days is roughly 42 calendar days — six weeks of cash flow, not four. If a customer’s AP department works in business days and you plan in calendar days, every invoice is late by your reckoning and on time by theirs.

Counting from the wrong start date

Invoicing on the 3rd for work delivered on the 28th of the previous month, then counting Net 30 from the delivery date, quietly gives away five days. Count from the date printed on the invoice unless the contract says otherwise.

Letting the due date land on a weekend and doing nothing

Bank transfers do not settle on a Saturday. A due date of Saturday means, in practice, Monday — so an invoice tracked as one day late on Sunday was never actually late.

Using end-of-month terms without saying which month

"Net 30 EOM" means the 30th day after the end of the invoice month, which for a 2 January invoice is 2 March — two months of credit, not one. Spell it out or use a plain day count.

Frequently asked questions

Does Net 30 mean 30 calendar days or 30 business days?

Calendar days, unless the contract explicitly says business days. Net 30 on an invoice dated 15 January is due 14 February. If you want business days, write "30 business days" — the two are about two weeks apart and assuming the wrong one is a common cause of aging disputes.

When does the clock start — invoice date or delivery date?

Conventionally the invoice date, which is why it is printed on the document. Some contracts start from delivery, or from receipt of a correct invoice, which can be materially later if the first invoice was rejected for a missing PO number. Whichever applies, state it in your payment terms.

What happens if the due date falls on a weekend or public holiday?

Most terms move payment to the next business day, since banks do not settle at weekends. Some move it back to the previous business day so the payer is not late. Both conventions are in use — the calculator supports either, and shows the unadjusted date alongside so the change is visible.

What is "2/10 net 30"?

A 2% discount if paid within 10 days, otherwise the full amount at 30 days. It is an early payment discount rather than a payment term as such, and it is far more expensive than it looks — roughly 37% annualised. The early payment discount calculator works out that cost.

Can I charge interest as soon as the due date passes?

That depends entirely on your contract and your jurisdiction, and some regimes set a statutory entitlement and a grace period. This tool computes dates, not entitlements — check your terms and local rules before charging anything. The late fee calculator shows what a given rate would come to.

What are the most common payment terms?

Net 30 remains the default in most B2B trade, with Net 14 and Net 15 common among freelancers and smaller suppliers, and Net 60 or Net 90 usual with large corporate and public-sector buyers. Due on receipt is used for one-off work and new customers.

Turn the answer into an invoice

The result above transfers straight into the invoice generator — dates, amounts and terms already filled in. Free, no account needed.

Open the invoice generator

Sources & further reading

Related

Invoice types

Published · General information, not legal, tax or financial advice.