Working days for invoicing: how to compute Net 30, Net 60, and 'business days'

“Net 30” on an invoice looks like a clear contractual commitment. It isn’t. The 30 is calendar days in some interpretations, business days in others; starts at invoice date in some, at receipt date in others. Combine the ambiguities and a Net 30 invoice can have legitimate due dates 30 to 45 days after the work was done. This guide explains how to write and read these terms without leaving money on the table.

The four interpretations of “Net 30”

1. 30 calendar days from invoice date.Most common in B2B. Invoice dated Jan 1 is due Jan 31. Doesn’t matter what day of the week.
2. 30 calendar days from invoice receipt date.Less common but legal in many jurisdictions. Buys the receiver several days of grace if the invoice arrives by mail. Watch for this in pharma, utility, government contracts.
3. 30 business days from invoice date.Roughly 42-44 calendar days depending on holidays. Some European jurisdictions and certain consultancy contracts use this.
4. End of month + 30 calendar days.Sometimes written “EOM + 30” or “Net 30 EOM.” Invoice dated Jan 5 is due Mar 1 (end of January, plus 30 days). Common in European retail and wholesale.

Which holidays count?

“Business day” is jurisdiction-specific. US federal holidays differ from UK bank holidays differ from German Feiertage. State and provincial holidays further complicate.

Standard US business-day exclusions:

• Weekends (Sat/Sun).
• 10 federal holidays: New Year’s Day, MLK Day, Presidents’ Day, Memorial Day, Juneteenth, Independence Day, Labor Day, Columbus Day, Veterans Day, Thanksgiving, Christmas.
• State/local holidays — vary widely. Most contracts ignore these.

UK standard exclusions: weekends + 8 bank holidays per year. EU standard: weekends + 10-13 holidays per country.

The contract-language traps

Four pitfalls that turn 30 days into 45+:

1. Invoice timing

Work delivered Jan 1, invoice issued Feb 1, Net 30 from invoice date → payment due Mar 3. Two months for a one-month clock. Fix: state “Net 30 from work completion date.”

2. Receipt vs sent

Invoice sent Feb 1 takes 5 days to arrive by post. Net 30 from receipt → due Mar 8. Fix: send invoices electronically and explicitly mark invoice date as start of period.

3. Holiday weighting

Net 30 ending on Dec 25 doesn’t automatically extend to Dec 26. Some contracts say it does (“if the due date falls on a non-business day, payment is due the next business day”) — most don’t. Read the actual terms.

4. The “reasonable” clause

Many contracts allow “reasonable time to process” on top of the stated terms. This is essentially free option for the payer. Strike it from contracts you’re negotiating; if you can’t strike, define it numerically (e.g., “up to 3 business days”).

Calculating the due date

For calendar-day terms: invoice date + N days. Standard date arithmetic. Use our date difference calculator to confirm.

For business-day terms: skip weekends and the applicable holiday set. Our working days calculatorhandles the US and major-EU holiday calendars; for custom holiday sets you’ll need to adjust manually.

Worked example. Invoice dated Wed Mar 4 with “Net 20 business days” in the US:

• Mar 4 (Wed) is day 0 (the invoice date itself doesn’t count under most conventions).
• Day 1 = Thu Mar 5. Counting weekdays only.
• Day 20 = Wed Apr 1. (No US federal holidays land in March/early April; weekends skipped.)

Best practices for invoicing

• State terms in calendar days, not business days, unless your client’s industry universally uses business days. Calendar days are simpler and equally legal.
• Include the explicit due date on the invoice, calculated and shown as a date — “Due: April 1, 2026.” Don’t make the recipient do the math.
• Use ISO 8601 date format (YYYY-MM-DD) on invoices that cross borders. 02/03/2026 is February 3rd in the US and March 2nd in the UK — a five-week ambiguity. See our ISO 8601 glossary entry.
• Include late-payment terms. EU law mandates 8% above the central bank rate as the default late fee on B2B invoices (Late Payment Directive 2011/7/EU). US contracts vary by state.

Sources: EU Late Payment Directive 2011/7/EU; US Uniform Commercial Code §2-301 (payment timing); IRS Publication 583 (record-keeping for business invoices).