What is mobile data?

Mobile data (sometimes called cellular data) is the internet connection your phone uses when it is not on Wi-Fi. Anything that loads from the web, messages, maps, video, social feeds, app updates, uses data, and your monthly allowance is measured in gigabytes (GB).

UK plans split into three groups: pay-as-you-go (top up as you go, no contract), SIM-only (fixed monthly fee, no handset), and pay monthly with a handset. On all three, going over the allowance triggers extra charges, though many newer plans now slow you down rather than charge extra, which is much friendlier to the wallet.

Quick units guide. A megabyte (MB) is one millionth of a GB. One gigabyte (GB) is roughly equal to: 8 hours of standard-quality music, 1 hour of HD video, 4 hours of HD video calls, or 200,000 WhatsApp messages. UK MVNOs typically show plans from 1 GB up to "unlimited" (with a fair-use cap, often hundreds of GB).

How many GB do you actually need?

Tick what you do on mobile data (not on Wi-Fi at home or work). The calculator below sizes your monthly plan in real time and shows how much you would save by moving a single heavy activity to Wi-Fi.

Mobile data calculator

Size your monthly mobile data plan

Set the dials for each activity. Result updates live and shows the plan size to look for.

On mobile data each day, you spend roughly...

Monthly use

Across all your activities.

Plan size to buy

Biggest single drain

Data-rate estimates verified May 2026. Sources: Netflix and YouTube official help pages, Spotify bitrate guide, WhatsApp data-saving documentation. Plan-size pricing is the typical UK SIM-only market range for May 2026.

Where the gigabytes actually go

Not every app eats data at the same rate. The table below ranks the activities most likely to blow through a small or mid-sized monthly allowance. The numbers are the rough per-hour data cost on a modern phone, based on published rates from Netflix, YouTube, Spotify and WhatsApp.

Mobile data cost per hour for common activities
Activity Per hour Quick comparison
4K video streaming on a phone~4 GBBurns a 20 GB plan in 5 hours
Cloud gaming (GeForce Now, Xbox Cloud)~5 GBFaster than 4K video
HD video streaming on a phone~1.5 GBA full Netflix film in HD ~3 GB
Tethering a laptop, average use~1.5 GBWay more if you stream video on it
SD / mobile-quality video~0.5 GBSwitch on data-saver to force this
HD video calls~0.3 GBAudio-only calls ~0.03 GB
Online gaming on phone~0.5 GBBig initial downloads are separate
Social media scrolling with autoplay~120 MBTikTok and Reels are heavier than Facebook
Web browsing and email~60 MBNews sites with auto-play video creep higher
Maps and navigation~50 MBAlmost zero with offline maps
Music streaming (standard quality)~40 MBLossless audio is roughly 5x heavier
WhatsApp text messages~1 MBEffectively free; voice calls negligible

Per-hour rates verified May 2026. Sources: Netflix and YouTube help pages, Spotify bitrate documentation, WhatsApp data settings page. Real-world figures vary with quality settings and signal strength.

Eight settings that cut data use without changing your habits

Most data tips on the web ask you to do less. These do not: they change the dials behind the scenes so the same hours of streaming, scrolling and browsing use a fraction of the GB.

  1. 1Restrict app updates to Wi-Fi only. A single round of App Store or Play Store updates is regularly 1 to 2 GB. On iOS: Settings → App Store → Mobile Data → off. On Android: Play Store → Settings → Network preferences → Auto-update apps → Over Wi-Fi only.
  2. 2Cap streaming quality on mobile data. Netflix has a separate quality toggle for Wi-Fi and mobile. YouTube and Spotify have the same. Setting "Standard" or "Data Saver" cuts video use by 60 to 80% with almost no visible loss on a phone screen.
  3. 3Turn on the data-saver in the OS. Both iOS (Low Data Mode) and Android (Data Saver) throttle background sync, pause non-essential downloads and squash photo previews when on cellular.
  4. 4Download maps for offline use. A single Google Maps download of your city or holiday area cuts navigation data from ~50 MB per hour to almost zero.
  5. 5Disable autoplay in social apps. TikTok, Instagram, Facebook and X all autoplay videos while you scroll, which is the single largest data drain for many users. Each app hides the toggle in Settings → Data → Video autoplay.
  6. 6Switch off iCloud Photos / Google Photos backup on mobile. A holiday week of camera photos can quietly upload 5 to 15 GB if you leave it on. Both services have a "Wi-Fi only" toggle for backups.
  7. 7Use WhatsApp's "Low data usage" calls. One toggle deep in WhatsApp settings cuts voice-call data by roughly half with no quality loss most listeners notice.
  8. 8Use free Wi-Fi where it is safe. Most chains, transport networks and councils offer free Wi-Fi. Avoid logging in to banking or email on open networks, reserve it for streaming and downloads.

How to check what you have actually used

The most reliable way to know your true monthly usage is your provider's own app or web account, that figure is what your bill is based on. Both Apple and Android phones also keep their own counters, but they reset only when you tell them to, so the figure can cover many months unless you reset it at the start of each billing cycle.

On an iPhone

  1. 1Open Settings → Mobile Data.
  2. 2Scroll down to "Current Period" for the total since you last reset.
  3. 3Tap Reset Statistics at the bottom on the first day of each billing cycle.

On an Android phone

  1. 1Open Settings → Network & internet → SIMs → App data usage (wording varies slightly by manufacturer).
  2. 2Set the data-cycle reset date to match your billing date.
  3. 3Optionally set a data warning and a hard data limit, the phone will warn or cut off cellular when you hit it.

Unlimited plans and data rollover: which actually saves money?

Two pricing features dominate the UK market in 2026: truly unlimited data (with a fair-use cap, usually 600 GB to 1 TB per month) and data rollover, where the unused portion of your allowance carries into the next month.

  • ✓Unlimited data, offered by Vodafone, Three, Smarty and EE among others. Sensible if your calculator result above is over 40 GB per month or your usage is unpredictable.
  • ✓Data rollover, Sky Mobile is the strongest UK example: unused data rolls over for several years on its piggybank-style plans. Useful if your usage is spiky (a heavy holiday month, then quiet ones).
  • ✓Speed caps on "unlimited", some of the cheapest "unlimited" plans cap speed at a few Mbps, fine for browsing but too slow for HD video. Always check the small print.

EU and worldwide roaming in 2026

Since Brexit, UK operators are free to charge for EU roaming and most now do. EE, Vodafone and Three reintroduced daily charges of roughly £2 per day in the EU on most plans, with some legacy and premium tariffs still including free or discounted roaming. O2 is currently the major outlier, with EU roaming included on most of its plans up to a fair-use limit.

Outside the EU, daily roaming charges climb sharply, £6 to £8 per day is a common rate, often with a tighter daily data allowance. Two practical alternatives:

  • ✓Add an eSIM travel plan for the country you are visiting. Several apps (Airalo, Holafly, Saily) sell prepaid local data eSIMs from £3 to £20 for a trip; usually much cheaper than the carrier daily charge.
  • ✓Use Wi-Fi at the airport, hotel and cafes for heavy tasks (video calls, photo uploads) and your home plan only for the basics in between.

Frequently asked questions

Ofcom reports average UK mobile data use of around 7 to 9 GB per active subscription per month, with a wide spread, light users on home Wi-Fi may use 1 to 2 GB, while heavy mobile-first users can exceed 50 GB. A 10 to 20 GB SIM-only plan fits the majority of UK users comfortably.

Usually not. Unlimited plans typically cost £15 to £25 a month, while a 20 GB plan covers most users for under £12. Unlimited makes sense if you stream a lot of HD video on mobile, tether your laptop daily, or have unpredictable monthly usage. For everyone else, sizing the plan to your real use saves £60 to £150 a year.

On older UK plans you would be charged out-of-bundle rates, often 10 to 20 times the per-GB cost of a bigger plan. Most modern SIM-only plans now slow the connection down instead (sometimes to a few Mbps) until the next billing cycle, which is much friendlier on the wallet. Always check whether your plan charges or throttles before signing up.

Not in itself, the same video stream uses the same data on either network. But 5G is fast enough to encourage heavier behaviour (4K streaming, cloud gaming, large downloads) that you might not bother with on 4G. The data is the activity, not the network generation.

Yes, both use mobile data when you are off Wi-Fi, but text messages are tiny (around 1 KB each) and won't move the needle. WhatsApp voice calls use roughly 0.5 MB per minute and video calls around 5 MB per minute, which adds up if you call abroad regularly.

The four most common culprits in order: a large app or game update on cellular, a new streaming habit (especially TikTok or Reels on autoplay), iCloud or Google Photos backing up holiday photos over cellular, and tethering a laptop or tablet. Check your phone's per-app data screen to find the spike.

Next steps

Once you know the plan size you actually need, compare SIM-only deals from across the UK market, they are the cheapest way to right-size your data without committing to a handset contract. If you want to keep your existing number, our switching guide shows how the PAC code process works in one working day.

For more, see our other UK mobile guides.