How much data you get roaming in the EU on a prepaid SIM

First, check what kind of prepaid you have

The prepaid rule applies to one type of tariff only. The EU implementing regulation on fair use, number 2016/2286, defines a prepaid tariff as one where your services are paid by deducting credit, per unit, that you loaded in advance. BEREC, the body of EU telecom regulators, adds in its roaming guidelines that only prepaid tariffs charged per unit count, and that other offers sold to prepaid customers, such as those that include a bundle of services, should not be treated as prepaid tariffs for this purpose.

So two cards that both say prepaid can follow different maths. A card where each megabyte comes out of your balance uses the credit formula below. A card where you pay for a pack with a set number of gigabytes each period falls outside the credit formula, and the operator may assess it under the rule for open data bundles, which our guide to the EU fair use policy explains.

The formula in Article 4(3), in plain words

Article 4(3) of the regulation lets the operator of a per-unit prepaid tariff limit the data you use in other EU countries at home prices. The limit has to be at least the volume you get by dividing the remaining credit, excluding VAT, that you have already paid and have available when roaming begins, by the regulated maximum wholesale roaming charge per gigabyte.

Two details matter. The credit counts without VAT, so if your balance is shown with tax included, take the tax out first. And the wholesale charge is a cap set in EU law that falls step by step over the years, so the same balance buys a slightly larger minimum as time goes on. Our roaming calculator shows the cap currently in force.

This volume is an alternative to asking you for proof that you live in the country. BEREC says that when an operator applies it, it cannot also apply a fair use policy based on residence or stable links.

BEREC's worked example

BEREC illustrates the rule with round, assumed figures: 20 euros of credit without VAT and a wholesale cap of 2 euros per GB. The minimum roaming volume is therefore 10 GB. What happens next depends on how much data that credit buys at home.

In the first case, the tariff charges 1 cent per MB, so the 20 euros buy 2 GB at home. The minimum of 10 GB is larger than anything the credit can buy, so no fair use limit applies at all: abroad, the customer spends credit exactly as at home.

In the second case, the tariff charges 0.05 cents per MB, so the same credit buys 40 GB at home. Now the operator may stop the home price at 10 GB of roaming data and add a surcharge beyond it. Read your own card the same way: the cheaper your data per megabyte, the more likely the credit formula is to bite.

When it is calculated, and why topping up helps

BEREC says the limit is calculated at the moment you start roaming, when you cross the border out of your home country, using the credit you have when you start using data roaming. If you top up while you are travelling, the operator should recalculate the volume with the new balance, and BEREC considers it good practice to tell you it has done so.

Two things eat into the result. Calls and texts paid from the same credit reduce what is left for data on that trip, whatever the data limit says. And the figure you get must be stated in the personalised pricing message your operator sends the first time you use data roaming in each country, which our guide to the roaming welcome SMS explains line by line.

Going over the limit

Going past the prepaid volume allows the operator to add a regulated surcharge on data only, not on calls or texts, for whatever you use beyond the limit, and that surcharge is capped by the same wholesale charge plus VAT. On a prepaid card the surcharge simply comes out of your credit faster, so the balance runs down sooner than you expect.

None of this applies outside the EU and the EEA countries Norway, Iceland and Liechtenstein. In Switzerland, the United Kingdom or Andorra, a prepaid card from an EU operator is priced by its own tariff; our guide to roaming outside the EU covers those cases.

If your prepaid falls short for the trip

• Top up before you leave, not on arrival: the limit is worked out with the credit you have when roaming starts.
• If you top up abroad, check the operator's message for the recalculated volume.
• Save heavy downloads, backups and video for Wi-Fi.
• Ask your operator whether it sells a roaming add-on for the EU.

The other route is to split the jobs: keep the prepaid line on for calls and texts, switch off its data roaming as in our guide to turning off roaming on your home line, and put the data on a separate eSIM. A Snoozim pack is data only, is paid once before the trip, and starts counting at the first connection in the destination; your number stays on the prepaid line for WhatsApp and bank codes.