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Extra charges for data over your limit: best and worst networks

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We compare the cheapest and most expensive UK mobile networks for extra data costs on your bill if you go over your monthly allowance. SIM Sherpa is your trusty guide. Last updated: 18th March 2021.

Going over your data limit

Different ways of charging for going over data allowances

Some cogs

When you first sign up to a pay monthly deal, you basically have to estimate how much data you’ll use. And if you end up needing more in the month, you’ll have to pay extra to keep using data (or turn it off and stop).

The way mobile networks charge for extra data outside your plan varies from provider to provider. The simplest (but rarest) way is charging per extra MB or GB you use onto your bill. The cheaper the rate, the better.

You also find some networks want you to buy a chunk of spare data for a set fee (called passes / add-ons / bolt-ons). You then chip away at that. The best last forever and sit there ready to be used when needed.

Similarly, other companies make you buy a monthly data add-on for an extra cost. These then keep renewing until you say stop. If you only need one-off data, you could forget and keep paying by accident.

In this guide, we take you through which of the options each networks offer and how they compare vs other providers on price and convenience.

How the networks compare

Our favourite network for extra data charges is SMARTY

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We think Three’s low-cost sub-brand SMARTY deal with extra data in the fairest, simplest way. If you run out of data, you just buy an Add-on. These currently cost £1 per GB, which you buy by topping up with credit.

£1 per GB is a much better rate than other networks. And the add-on never expires. So if you were only short 50MB near the end of the month, you buy one, continue using your phone and keep the rest for the future.

Another good thing about SMARTY is that your plan is only on a 1-month rolling deal anyway. So if it looks like you’ve got too little data on a regular basis, you can just move up to a bigger one with enough in it.

Useful link: Our full SMARTY review

VOXI, Tesco Mobile and Sky are also decent choices

VOXI logoTesco Mobile logoSky logo

One-off passes, fair prices

It’s another sub-brand we rate next best: VOXI, who are owned and operated by Vodafone. If you run out of data with them, you can either choose to buy your next month’s plan early or add a “data extra”.

These currently cost £3 for 1GB and they last for 30 days from the day you buy them (or until you burn through the data). That’s at the reasonable end of charges and you can move plans month-to-month.

Tesco Mobile offer one-off Data Bundles at 1GB for £5 (other smaller/larger increments available) if you run out. These last until your data refreshes and are much better value than paying as you go at 10p per MB.

It’s also worth looking at Sky Mobile. They’re more expensive than the others above, with a one-off block of 1GB data costing £6, but that’s still significantly cheaper than many other providers’ extra data rates.

Useful links: VOXI review | Tesco Mobile review | Sky Mobile review

BT, Three, iD Mobile and Plusnet offer monthly add-ons

BT Mobile logoThree logoiD Mobile logoPlusnet Mobile logo

Add-ons renew themselves each month

On paper, the next mobile networks can work out as cheap as the ones above for extra data charges. But you have to be careful, as they make you buy data add-ons, which renew every month if you don’t cancel them.

On Three, you can buy a 1GB data add-on for £5 a month if you run out. We’d put this ahead of Sky if it wasn’t for the fact that the add-on automatically renews. It’d be too easy to forget and keep getting charged.

It’s the same on Plusnet Mobile and BT Mobile, who both charge £6 for a 1GB data add-on that recurs monthly unless you cancel it. You can also pay as you go on both at 10p per MB if your new month starts very soon.

iD Mobile come in a little more expensive at £7 a month for an extra 1GB. This seems especially expensive with cheap networks like iD, where it could exceed the cost of your plan (or double it if you forget to cancel).

Useful links: Three review | BT Mobile review | Plusnet Mobile review | iD Mobile review

The big main networks are a little pricier on one-off basis

Vodafone logoEE logoO2 logo

More expensive than average

Vodafone are next. You can get a one-off block of 1GB for £8 to tide you over until next month. That's the most reasonable out of the big networks in this section.

EE are very similar. A one-time 1GB data pass costs £8.34 and lasts until your plan updates. You can get cheaper monthly add-ons but there’s always the risk of forgetting to cancel and paying more each month.

And O2 are more expensive, with their one-off bolt-on costing £12 for 1GB. Although to be fair to them, you can also get smaller chunks of data for less (we’ve chosen the 1GB to make comparison easier).

Running out of data on these networks gets expensive, fast.

Useful links: Vodafone review | EE review | O2 review

Virgin Mobile’s daily charge could work out expensive

Screenshot of Virgin's data charges

More expensive than original plan

While it’s cheap to join Virgin Mobile for your basic plan, going over your data allowance does get expensive fast. There’s a couple of ways you can pay:

Either they charge you £3 for up to 1GB usage a day, per day. So if you used 100MB today and 100MB tomorrow that would cost £6. Or if you used 1GB today and 1GB tomorrow that’d also be £6.

Or to avoid this, you can buy a one-off Data Add-On, priced at £10 for 1GB. These last until your data allowance refreshes, so become worthwhile if you’ve got over 3 days left.

Both ways we think will work out among the most expensive of any provider, unless you literally just have one day left and run out of data. You can change plans month-to-month on Virgin if you need a bigger one though.

Useful link: Virgin Mobile review

Only a few networks just let you pay per MB

giffgaff logoiD Mobile logoBT Mobile logoPlusnet Mobile logo

Just pay for what you use on these networks

When networks charge per MB, it can actually work out best, if you have just a short amount of time before your data renews anyway. But it can also work out expensive if the rate is high and you’ve got ages left.

At 10p per MB, giffgaff seems reasonable enough for small amounts of data for a short time. If you ended up needing 1GB more though, that’s £10 (at which point you’re better off just buying next month’s plan early).

And then on some of the networks we've already featured above, you can choose to just pay per MB, if it'll work out cheaper than buying a block of data. This makes sense if it's only a couple of days usage.

Those networks are iD Mobile, BT Mobile and Plusnet Mobile, who all charge 10p per MB and add it your bill (as long as you don't have a spending cap that would prevent this).

All other networks force you to buy an add-on if you want to keep your data working and don't let you just pay as you go per MB.

Useful link: giffgaff review

More network ranking guides

Full mobile network reviews