Invoice Due Date Calculator NZ
This invoice due date calculator tells you the exact day an invoice falls due under the payment terms you have agreed, so you can put the right date on the invoice and know when to start chasing it. Payment terms are written in shorthand that is easy to misread. Seven, fourteen and thirty days count calendar days from the invoice date. The 20th of the month following means the 20th of the next month, however late in this month you invoice, so an invoice sent on the 1st waits far longer than one sent on the 31st. End of the month following runs to the last day of the next month. Twenty working days skips weekends and public holidays, which matters around Christmas, Easter and Labour Day. You enter the invoice date and choose the terms. The calculator gives you the due date and its weekday, the number of calendar days from the invoice date to the due date, and whether that day is a working day. When it falls on a Saturday, a Sunday or a national public holiday, it shows the next working day as well. Public holidays are counted on their observed dates for 2026 to 2028 and into early 2029. Regional anniversary days are not included, because they differ from region to region.
From the same team as Calculate.co.nz
Your Timesheets at jobtracker.co.nz logs your hours on a week grid or a timer that keeps counting when your phone locks, free on every plan. Career and Timesheets turns those hours into projects and rates, fixed fees and retainers, numbered invoices with GST only when you are registered, expenses and mileage, and the tax to set aside, from $4.99 a month billed yearly.
Log your hours freePayment terms are usually set by the agreement between you and your client, and some contracts, such as construction contracts, are also covered by their own legislation. Working days here skip weekends and national public holidays only; a regional anniversary day in the period adds a day.
How it works
Day terms add that many calendar days to the invoice date, so 30 days from 5 October is 4 November. Terms of the 20th of the month following set the due date to the 20th of the month after the invoice month, and end of the month following sets it to that month's last day. Twenty working days counts forward from the day after the invoice date and skips every Saturday, Sunday and national public holiday on its observed date. The calendar days are the plain count from the invoice date to the due date. If the due date is a Saturday, a Sunday or a public holiday, the calculator steps forward one day at a time until it reaches a working day and shows that date as well. Payment terms are usually a commercial agreement: whether a payment due on a holiday may be made on the next working day is part of what you and your client agreed.
Worked example
An invoice dated Monday 5 October 2026 on terms of the 20th of the month following is due on Friday 20 November 2026, 46 calendar days later, and that is a working day. The same invoice on 20 working days terms is due on Tuesday 3 November 2026, 29 calendar days later, because Labour Day on Monday 26 October is skipped along with the weekends. The table shows every term for the same invoice date.
| Terms | Due date | Calendar days |
|---|---|---|
| 7 days | Monday 12 October 2026 | 7 |
| 14 days | Monday 19 October 2026 | 14 |
| 20th of the month following | Friday 20 November 2026 | 46 |
| 30 days | Wednesday 4 November 2026 | 30 |
| End of the month following | Monday 30 November 2026 | 56 |
| 20 working days | Tuesday 3 November 2026 | 29 |
None of those dates is a weekend or a holiday. An invoice dated 25 November 2026 on 30 day terms is different: it falls due on Friday 25 December 2026, Christmas Day, and the next working day is Tuesday 29 December 2026, because Monday 28 December is the observed Boxing Day.
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