Everyday NZ guide · New Zealand
28-Day vs Monthly Mobile Plans NZ
Compare 28-day and calendar-month mobile plans in New Zealand, including 13 annual renewals, yearly price, promotions, included data and renewal timing.
Reviewed 26 August 2026
Reviewed by KiwiTools editorial team — NZ consumer researchers using government, regulator and provider sources
General information only. School-zone boundaries and enrolment schemes can change; verify the exact address with current Ministry and school information.
Key points
Compare annual mobile-plan cost
A 28-day plan covers 364 days after 13 renewals, while a calendar-month plan normally renews 12 times yearly.
Multiply the displayed 28-day price by 13 before comparing it with a monthly price multiplied by 12.
Also compare included data, speed limits, rollover, promotions and add-ons over the same period.
28-day and monthly renewal arithmetic
This comparison uses a $30 displayed renewal price for both plans and excludes promotions or extras.
| Check | Renewals in about one year | Annual cost | Average monthly equivalent |
|---|---|---|---|
| $30 every 28 days | 13 | $390 | $32.50 |
| $30 per calendar month | 12 | $360 | $30.00 |
A 28-day plan renews thirteen times in an ordinary year
$30 every 28 days costs about $390 across 13 renewals. A $30 calendar-month plan costs $360 across 12. The matching sticker price hides a $30 annual difference.
Convert both to annual cost or average monthly equivalent before comparing data. The Commerce Commission specifically highlights the thirteenth-payment confusion.
The renewal date walks backwards through the calendar
A 28-day plan renews every four weeks, so the date moves earlier relative to calendar months. Someone paid monthly can face two renewals inside one pay-to-pay budget window.
Automatic renewal needs enough credit or a valid payment method on the actual date. A failed renewal can also break rollover eligibility or a consecutive-renewal promotion.
Read the related prepay vs pay monthly mobile guideRead the related mobile data rollover guideRead the related one nz mobile plans guide
More renewals can also mean more data
If both plans include 10 GB per renewal, the 28-day plan supplies roughly 130 GB across 13 cycles versus 120 GB across 12 months. The extra payment is not pure waste when the allowance is genuinely used.
Compare annual cost per useful GB, not advertised GB. A person using 4 GB a month gets no value from repeatedly expiring surplus.
Frequently asked questions
How many 28-day renewals are in a year?
Thirteen periods cover 364 days, so continuous service normally involves about 13 renewals.
Is a 28-day plan the same as monthly?
No. Calendar months vary in length and normally create 12 renewals yearly.
How do I compare annual cost?
Multiply a 28-day price by 13 and a monthly price by 12, then add promotions, extras and device costs.
Does a 28-day plan also provide more data yearly?
It can provide 13 allowances, but actual value depends on use, expiry and rollover rules.
Put the guide into practice
Continue with related KiwiTools calculators
Test your own numbers, compare scenarios and return to the guide to check assumptions and limitations.