What this calculator works out
This calculator multiplies daily data use by the number of days, adds an overhead allowance, and converts the total to gigabytes.
The overhead accounts for the difference between the data an app reports and the data your allowance is charged for — protocol headers, retries and background activity all add to the total.
Enter your details
Before you choose an allowance
- Check your actual usage first. Both Android and iOS report data used per app and per billing period.
- Video dominates. Streaming at high definition uses roughly ten times as much as music, and far more than everything else combined.
- Wi-Fi use does not count towards a mobile allowance. If most viewing happens at home, mobile usage may be much lower than expected.
- The 10% overhead is a reasonable default; heavy streaming and video calling push it higher.
Rough hourly figures: standard-definition video around 0.7 GB, high definition 3 GB, 4K considerably more; music streaming 0.07 to 0.15 GB; video calling 0.5 to 1.5 GB; social media scrolling with autoplay video 0.5 to 1 GB. Messaging, email and browsing are negligible by comparison — a month of them is less than an evening of HD video.
How this calculator works
Daily use scaled to the period, plus overhead:
Total MB = daily MB × days × (1 + overhead ÷ 100)
GB = MB ÷ 1,024Dividing by 1,024 uses the binary convention, which is how devices report storage and data. Network operators generally use decimal gigabytes of 1,000 MB, so an operator's figure will differ slightly from a phone's — around 2.4% for a gigabyte.
Worked example: 500 MB a day
Using the default figures — 500 MB a day over 30 days with a 10% overhead:
- Total: 16.11 GB
Just over 16 GB, which sits awkwardly between common 15 GB and 20 GB allowances. That is a useful thing to discover before committing to a contract — 500 MB a day is around half an hour of standard-definition video, which is a modest habit rather than a heavy one. Switching to high definition would take the same half hour to roughly 45 GB a month.
Common mistakes
- Estimating rather than checking. Both phone platforms report actual usage by app.
- Counting Wi-Fi use. Only mobile data counts against the allowance.
- Forgetting background activity. Updates, backups and syncing all consume data.
- Ignoring video quality settings. Capping streaming quality is the single largest saving available.
- Assuming an operator's GB matches a phone's. Decimal and binary gigabytes differ by about 2.4%.
Frequently asked questions
How do I check my actual usage?
On iOS, Settings then Mobile Data shows usage by app since the counter was last reset. On Android, Settings then Network and internet then Data usage gives the same by billing cycle. Both let you set a warning or a hard limit, which is a more reliable safeguard than watching the figure.
How can I use less?
Cap streaming quality in each app's settings — the single largest saving. Download music and video over Wi-Fi for offline use. Restrict background data for apps that do not need it. Turn off autoplay video in social media apps, which quietly consumes a great deal.
What happens if I go over my allowance?
It depends on the tariff. Some operators charge for additional data, some slow the connection until the next cycle, and some block data entirely until you buy more. Out-of-bundle charges can be substantial, so it is worth knowing which applies before it happens.
Does roaming use the same allowance?
It varies. Many UK operators reintroduced roaming charges for European travel after 2021, some with a daily fee and some with a capped allowance. Outside Europe, charges are generally much higher. Check your specific tariff before travelling — this is an area where assumptions are expensive.
Is what I enter stored?
No. Figures are processed in your browser and never transmitted or retained.
Related tools
References
- GOV.UK — consumer rights on mobile contracts and roaming charges
- MoneyHelper — guidance on mobile phone contracts and reducing bills
Sources are checked at publication and can change — how I choose and check references.