Is 100GB of Data Enough?

100GB covers more usage than most heavy users ever reach, and it frequently costs less than unlimited from the same network. This guide explains what 100GB realistically covers, when it falls short, and how to judge whether unlimited is worth the difference.

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Reviewed by: Phil Brown, founder of SIM Only Finder. Phil previously worked in UK mobile retail at Three UK, advising customers on SIM plans, contracts, and network choices. He has spent over a decade running consumer comparison platforms and reviews networks and SIM-only deals based on that hands-on industry background. About the author

Last reviewed: July 2026. Updated regularly to reflect current plan pricing, network changes, and roaming policies.

How we put this guide together

To put this guide together, we reviewed large allowance and unlimited plans across the main UK networks and MVNOs, comparing how the 100GB tier is priced against unlimited from the same provider and checking fair usage and tethering terms directly against each network's published terms. Usage figures are estimates based on published app and network guidance, since actual consumption varies with video quality, handset, and caching.

Quick answer: is 100GB enough?

For almost everyone, yes. 100GB covers heavy daily video streaming, a long commute without Wi-Fi, and regular tethering, and still leaves headroom for most users.

The people who genuinely exceed it are those using mobile data as a full home broadband replacement, or tethering multiple devices for extended periods. If that is not you, unlimited is buying insurance against something that will not happen.

What 100GB actually covers in a month

Across a month, 100GB is roughly equivalent to any one of the following in isolation.

• Around 100 hours of standard definition video streaming
• Around 30 hours of high definition video streaming
• Around three hours of high definition video every day of the month
• Substantial laptop tethering alongside normal phone use
• Effectively unlimited music, messaging, browsing, and navigation

Three hours of high definition video a day, every day, is the figure worth holding on to. Very few people sustain that on mobile data rather than Wi-Fi, which is why 100GB is sufficient for the overwhelming majority of heavy users.

Who 100GB suits

100GB is the right tier for daily commuters who stream on the move, people who tether a laptop regularly for work, households where mobile data supplements patchy home broadband, and anyone who has previously exceeded a 50GB allowance.

It also suits people who want the practical freedom of unlimited without the price. In day to day use the experience is identical, because the ceiling is high enough that you never approach it.

Best for: Heavy users and regular tetherers who want unlimited-style freedom at a lower monthly cost, and who have never actually run out of data on a large allowance.

100GB compared with unlimited

The comparison comes down to whether the price difference buys you anything you will use. On most networks, unlimited carries a premium over the largest fixed allowance. Across a 24 month contract that difference accumulates into a meaningful sum, and for most people it purchases data that is never consumed.

There is a second point that surprises people. Unlimited plans are not without limits. Fair usage policies allow networks to reduce speeds at very high consumption, and tethering is sometimes capped separately even when the main allowance is not. Our guide to whether unlimited data is really unlimited sets out where those thresholds sit on each network. In several cases the tethering cap on an unlimited plan is lower than a 100GB allowance would give you outright.

That said, pricing at the top of the market moves. There are periods when a promotional unlimited plan undercuts 100GB from the same network, at which point the decision makes itself. It is always worth comparing both on our unlimited data SIM only deals page before committing to either.

When unlimited is the better choice

Unlimited earns its price in three situations. The first is genuine unpredictability, where some months are quiet and others are very heavy, making any fixed allowance either wasteful or insufficient.

The second is using mobile data as a primary connection rather than a supplement, whether because there is no fixed broadband at the property or because the broadband is unreliable. The third is professional dependence, where running out of data would stop you working and the cost of that outweighs the monthly difference.

Outside those cases, the honest test is whether you have ever actually exhausted a large allowance. If you have not, 100GB is the better value choice.

What to look for in a 100GB plan

At this tier, the headline allowance matters less than the surrounding terms, because the allowance itself is rarely the binding constraint.

Check the tethering terms first, since that is the most common reason people need a large allowance in the first place. Then check whether the network applies annual mid-contract price rises, because at this price point an annual increase compounds into a significant sum over two years. Our guide to SIM only mid-contract price rises covers which networks raise prices and which hold them flat.

Roaming caps are also worth reading at this tier. Networks that include EU roaming almost always apply a fair usage limit well below 100GB, so the allowance you can actually use abroad is smaller than the headline figure.

If you are not certain 100GB is the right size, a 30-day SIM only deal is a low risk way to find out before committing to a long contract. And if you are weighing this tier against something smaller, our guide to whether 30GB is enough covers where the middle of the market sits.

FAQs

How long does 100GB of data last?

For heavy mixed use including daily video streaming and regular tethering, 100GB typically lasts a full month with headroom. It is difficult to exhaust without using mobile data as a home broadband replacement.

Can 100GB replace home broadband?

For one light user, possibly. For a household streaming video on multiple devices, no. Home broadband use routinely runs into hundreds of gigabytes a month, so a fixed mobile allowance is rarely a like for like substitute. Check the tethering terms carefully if you plan to try.

Is 100GB cheaper than unlimited?

Usually, though not always. Most networks price unlimited at a premium over their largest fixed allowance, but promotional unlimited pricing sometimes closes or reverses that gap. Compare both from the same network before deciding.

Does data rollover matter at 100GB?

Less than at smaller allowances, because you are unlikely to be short in any given month. It is still a useful feature if your usage is uneven, and our guide to which networks offer SIM only data rollover covers who provides it.

Conclusion

100GB is enough for the vast majority of heavy users, and it usually costs less than unlimited from the same network. The practical experience is the same, because the ceiling sits above where normal usage reaches.

Choose unlimited if your usage genuinely varies month to month, if your phone is your primary internet connection, or if running out would stop you working. Otherwise the sensible approach is to compare both tiers on total cost across the contract, including any annual price rises, and take the cheaper one.

How to choose between 100GB and unlimited

1. Check whether you have ever run out. Look at three months of usage in your network app. If your peak month sits well below 100GB, the fixed allowance is enough.
2. Compare both tiers from the same network. Price the 100GB plan and the unlimited plan side by side rather than assuming a gap exists.
3. Read the tethering and roaming terms. These differ more between plans than the headline allowance does, and they are usually the terms that actually bind.
4. Total the cost across the contract. Include annual price rises where the network applies them, since they compound at this price point.
5. Keep your number when you switch. Our guide to keeping your number when switching to SIM only covers the PAC process.

Editorial policy

This guide is produced by SIM Only Finder to help heavy data users compare large allowances and unlimited plans across UK networks. Network terms, pricing, and plan availability are checked regularly and updated to reflect current offers. Always confirm current terms directly with the network before signing up.