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Almost every data question comes back to one thing: how much is enough without overpaying. The answer is not driven by the number of days in the trip but by how you use the connection during them. Two people travelling together for the same week can differ several times over, because one is reading maps and sending messages while the other streams video on the train every day.

This section explains what really consumes data, what unlimited means in practice, and the handful of settings that visibly stretch the same plan further. For the actual figures — the allowance, the validity and what happens once you pass it — read the plan page itself, because those terms differ by destination and by supplier.

Start from behaviour, not from the number of days

The estimate that works is to look at your own usage over the past week. Both iOS and Android keep a data summary inside the cellular menu, and that figure is a far better starting point than a guess, because it reflects your habits rather than those of an imaginary traveller.

Then adjust for the shape of the trip. A hotel-based holiday with Wi-Fi in the room and a lot of walking uses less than people expect. A trip spent navigating all day, taking calls, or letting photos and video upload to the cloud uses more — often more than the same person uses at home.

What actually consumes the most

The ranking below is relative, not a figure per hour, because the real volume depends on video resolution, signal quality and each app's own settings. What is useful is knowing which activities sit in the heavy group and should be the first ones you rein in.

Working out a number before you go

1. 1Read your recent usageOpen the data summary in the cellular menu and take the total for the most recent period. Divide by the number of days to get your own daily average.
2. 2Subtract what Wi-Fi will coverIf your accommodation has Wi-Fi and you will be there for several hours a day, take that share out — but not too much of it. Hotel Wi-Fi is often not steady enough for anything that needs a continuous connection.
3. 3Add what only happens while travellingNavigation, translation, ride-hailing and looking places up happen far more often on a trip than at home. Always add an allowance for it.
4. 4Leave room for the day that goes wrongA delayed flight, an address you cannot find, or an unplanned call all spike usage in a single day. A margin is cheaper than scrambling for a top-up abroad.
5. 5Match it against the plans that existCompare the result with the allowances and validity on that destination's plan pages, and round up one step if you are in the heavy-use group.

Work out how much data to buy

What unlimited actually means

A plan described as unlimited generally means unlimited in volume, not constant in speed. Most suppliers set a full-speed allowance per day or per cycle; once you pass it the connection is slowed until the next cycle begins. That condition is usually labelled a fair use policy, or FUP.

So the line to read is not the word unlimited in the heading but the two lines underneath it: how much runs at full speed before the throttle, and when the cycle resets. Those vary by plan and destination, which is why they sit on the plan page rather than being summarised here.

What still works after a throttle

When the throttle applies, the connection is slowed rather than cut. Tasks that move little data and do not need continuity usually still behave normally; anything that has to move a lot of data continuously becomes obvious at once.

Usually still fine

Text messaging, email without large attachments, text-led web pages and navigation using a map you already downloaded all keep going at reduced speed.

Usually not viable

High-resolution video, video calls, large uploads and app downloads slow to the point of being unusable. If you must do any of them, wait for Wi-Fi or for the next cycle.

When a daily plan resets

A daily plan issues a fresh allowance on a cycle the supplier defines. Some count from the moment of first activation; others reset at midnight in a fixed time zone, which may not be the local time where you are standing. That mismatch is why the first day sometimes feels unusually short.

To plan around it, check how the plan page defines the cycle, then put the heavy activity at the start of a cycle rather than the end.

Can two people share one plan?

Yes, through a hotspot: the handset holding the profile shares its connection with the other device. Two things to keep in mind. Everything comes out of the same allowance, and some plans set different terms for sharing than for use on the device itself. Check the plan page before you build a trip around it.

In practice sharing suits a pair who stay together. If you are splitting up during the day, two separate plans are usually easier: the hotspot handset has to stay within range, and its battery drains noticeably faster.

Data disappearing while the phone sits in your pocket

A phone does not stop working when it goes back in your pocket. Apps keep syncing mail, uploading photos, checking for updates and pulling location data. On home Wi-Fi nobody notices. On a metered travel plan, that is the share that vanishes without explanation.

• Turn off automatic photo and video backup, or restrict it to Wi-Fi
• Set app updates to Wi-Fi only
• Disable video autoplay in social and news apps
• Download the maps, music and video you will want in advance
• Switch off background refresh for apps you do not need on the trip
• Leave the system data-saver mode on for the whole trip
• Look at the usage figure in the cellular menu every couple of days

Checking the remaining balance sensibly

The figures you can see come from different places and do not update at the same moment. Knowing where each one comes from removes most of the confusion when two of them disagree.

Using a VPN on an eSIM

A VPN works as normal. It sits on top of the connection, so whether the SIM is plastic or embedded makes no difference. Two practical notes: encryption adds a little overhead to everything you send, and latency rises if the server you pick is far away.

The caution is that some countries regulate or restrict VPN use. That is a matter of local law rather than of the plan. Check the destination beforehand if your work depends on one.

Why the plan has no phone number

Most travel plans are data-only, which is why they carry no number for calls or texts. That shape is what keeps them inexpensive and instantly installable, without tying the purchase to a local number registration.

The consequence to plan around is that verification texts still arrive only on your home SIM, so keep it in the phone and leave it able to receive SMS. For calls, use an app that places them over the internet; those run on the plan's data like anything else.

When the allowance runs low mid-trip

Start by comparing what is left against how many days remain. If the gap is real, cut the heavy activities first, then look at topping up or buying again. Which of those is possible depends on the plan you hold: some can be topped up, others have to be repurchased.

If you are not sure which kind you have, send us the order number on LINE at https://lin.ee/skDPoNx or by email at esimonline.asia@gmail.com and we will check. We will tell you the options that exist for that plan, not the general ones.

Arrival and departure days use more than you expect

Travel days are the peak of the whole trip, because everything happens at once: finding the way out of the airport, booking a ride, opening the map, locating the accommodation, telling people at home you landed, and every app syncing at once after a flight spent offline. That is why the first day so often feels as though the allowance vanished, when in truth a travel day simply looks like that.

The way to handle it is to do what you can in advance, on Wi-Fi: download the city map, save the address of your accommodation for offline use, and restrict photo backup to Wi-Fi before you board. Those three take most of the weight off the first day and make the rest of the trip's balance easier to read.

See regional plans for multi-country trips