28 day vs 30 day expiry: Why it matters

Alex Kidman 7 March 2016

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Some mobile providers are shifting to prepaid plans with 28-day expiry. How much more will you pay as a result, and might you actually be better off?

amaysim recently made headlines by changing its UNLIMITED mobile deals and significantly upping the data quota on each plan. Its most popular plan, UNLIMITED 5GB, is changing to UNLIMITED 7GB gaining an extra 2GB of data.

On the surface, that seems like a win for consumers, except at the same time amaysim also altered the expiry time of each of those plans down from 30 days to 28 days.

amaysim is hardly alone in this respect; many providers have plans with 28-day expiry periods rather than 30 days. Some providers keep matters rather vague by referring to a "month" of subscription to prepaid services, but if you dig deep enough most still think of a month as being a 30-day span. If they switch to a 28-day deal, that means you do rather better in February but slightly worse in January, March, May, July, August, October and December. Plans which have a 28-day expiry include Telstra's Freedom, Optus My Prepaid Ultimate and Vodafone's Combo plans.

So what’s the problem with a 28-day expiry period versus a 30-day one, aside from the rather obvious fact that you’re getting two less days?

The big issue how many times you need to recharge over a year or longer. Mobile number portability means it's easy to switch carriers, but the reality is that most of us are rather lazy, and tend to stick to our existing plan rather than seeking out new deals. That means anyone jumping onto a 28-day plan will probably use that plan for longer than a single recharge period.

Let’s use some mathematical examples to show how this plays out over a year’s worth of recharges for a fictional provider with a $20/month plan that switches from 30 days of expiry to 28 days without altering the plan cost. The following table shows how much you’ll pay over a year when these switches are made.

Fictional Telco Plans30-day expiry28-day expiry
Cost of recharge$20$20
Number of recharges in a year (365 days divided by Expiry)12.1666666713.03571429
Total yearly cost$243.33$260.71

As you can see, the loss of two days in each recharge period adds up over a year to nearly as much as the cost of a full additional recharge; this would apply whether you were paying $20 per month or any other sum.

Count data per day, not number of days

That isn’t to say that a 28 day plan is automatically a "bad" choice. You have to weigh that shorter expiry period against the inclusions on the plans. With most plans in Australia now offering unlimited calls and texts to Australian numbers, data is going to be the main battleground, and the most useful measure is how much data you can use each day on the plan.

For instance, the old amaysim UNLIMITED 5GB plan offered an average of 166MB per day (5000MB divided by 30). The updated 7GB plan offers 250MB per day, so you're actually getting more data for your money. Here's how much data per day you get with a number of plans all costing around $40 a month and offering unlimited calls:

PlanDataExpiryCostNetwork
Optus My Prepaid Ultimate4GB28 days$40.00Optus 4G
Telstra Freedom Plus3GB28 days$40.00Telstra 4G
Vodafone Combo4GB28 days$40.00Vodafone 4G
amaysim UNLIMITED7GB28 days$39.90Optus 4G
Kogan 5XL5GB30 days$36.90Vodafone 3G
TPG T4G III5GB30 days$39.99Vodafone 4G
Boost UNLTD3GB30 days$40.00Telstra 4G
Vaya Unlimited XL7GB30 days$34.00Optus 4G

You can check the full details of competing plans, including their expiry periods, with our Mobile Phone Finder to find the plan that best suits your needs. We've pre-populated the table below for a moderate-use prepaid plan, but you can adjust to suit your particular needs by clicking on "Modify Results" to change the data or call inclusions:

Image: Shutterstock

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