How much mobile data should you buy for a trip?
Your recent usage is a better starting point than a universal “GB per day” claim. The examples here are budgeting arithmetic, not measured promises about app consumption.
By Simvito · Published · Reviewed and updated
Start with a comparable day
Check mobile-data use by app in your phone’s settings and note the measurement period. Choose days when your Wi-Fi access resembled the trip. A home day spent entirely on Wi-Fi is a poor estimate for sightseeing.
Include navigation, messaging, uploads, video calls and any laptop tethering you expect. App settings, resolution, background updates and downloaded maps can change the result substantially.
Build a budget
- Estimate mobile data per day from your own usage, then multiply by the number of days you need coverage.
- Add an explicit reserve for changes of plan. For example, 0.4 GB × 7 days = 2.8 GB; adding a chosen 25% reserve gives 3.5 GB. The 25% is an example assumption, not a network requirement.
- Round up to an available allowance only after checking validity, network and post-allowance behaviour. A cheaper plan that expires halfway through is not a substitute.
Daily or total allowance?
A daily plan suits fairly even usage, but unused daily data may not carry over; check its reset terms. A total-data plan shares one allowance across the valid period and can suit uneven days.
For example, a 1 GB-per-day plan and 7 GB total are not equivalent if you need 3 GB on one day. Also compare what happens after the allowance: reduced speed, stopped data or an unconfirmed rule.
Plan for video and hotspot separately
Download large files and app updates over Wi-Fi where possible. Set cloud-photo backup and automatic downloads to Wi-Fi if they are not needed on mobile data. Check a video app’s own quality setting before a long session.
If your plan supports personal hotspot, sharing with a laptop uses data much faster than a phone alone, and the speed depends on the local network. “Unlimited” also does not by itself promise a particular speed.
Apply the budget to a real plan
For a week in Japan, use the Japan eSIM catalogue to compare total and daily allowances. The Japan 10 GB / 7-day plan details give one concrete example: the total allowance is shared across the whole validity period, rather than renewed each day.
The 3.5 GB budget calculated above fits within a 10 GB total allowance, but allowance alone does not determine which plan to buy. Check the current availability, price, available networks and start rule on the detail page, then compare other plans for your trip.
Choose and monitor
Use the catalogue to compare the actual allowance and validity. Check your device’s usage during the trip, remembering its counter may differ from the operator’s billing record.
It depends on the plan: some can add data within the current validity, some can add days, and some can't be topped up. The plan shows which before you buy. To top up, open the eSIM in My eSIMs or on its order page and choose an option; it goes onto the same eSIM, so there's nothing new to install. If no options are shown, buy a new plan.