The most useful estimate starts with your own mobile-data use, not a universal GB-per-day rule. Trip length alone cannot tell you the allowance you need: video calls, streaming, uploads, hotspot use and access to Wi-Fi change the answer.
Start with a measured daily average
Check mobile-data consumption over a period whose length you know. Divide the GB used by the number of days in that period. Use a period that resembles the way you expect to use your phone abroad.
On iPhone, check the per-app mobile-data statistics and the period they cover; see Apple’s mobile-data usage instructions. On Pixel, app data usage is available in the SIM settings; see Google’s mobile network settings guide. Menu labels differ across phones and software versions.
A worked planning example
Suppose you measured 4 GB over 8 days. That is 0.5 GB per day. At the same rate, a 10-day trip would use 5 GB. If you chose an illustrative 20% buffer, your planning allowance would be 6 GB.
Calculation: measured daily GB × trip days × your chosen buffer factor. The example describes arithmetic, not a claim that travellers usually use 0.5 GB per day or need a 20% buffer.
Adjust the estimate for your itinerary
- Will you have reliable Wi-Fi for large downloads, uploads and app updates?
- Will you use your phone as a hotspot for a laptop or another traveller? Check that the plan permits it.
- Will your travel days involve more video, navigation or calls than the measured period?
- Can you download maps and entertainment before leaving?
- Can you buy a top-up easily if the first allowance runs out, and what will it cost?
Fixed data or unlimited?
Compare the total price of a fixed allowance that meets your estimate with an unlimited plan that lasts for the same trip. Check how much data the unlimited plan provides at full speed, when that allowance resets, the reduced speed, and whether hotspot use has a separate limit. The word “unlimited” does not answer those questions.
If you expect heavy use every day, the full-speed allowance can matter more than the headline price. If usage is uncertain, a clearly priced top-up may be useful, but do not assume every provider offers one. See the published unlimited-plan limits and provider catalogues.
Compare plans that last long enough
An allowance can be large enough while the plan expires too soon. Set both trip length and minimum GB on the destination comparison. The 7-, 14- and 30-day examples on country pages are filter shortcuts with stated allowances, not recommendations for everyone.
For several countries, compare a regional plan with the separate allowances you would need at each stop. Check whether the regional allowance is shared across the whole trip and when its validity begins.