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How to tell if your wireless carrier is throttling data

Is your unlimited data plan really unlimited? Use an app to find out.

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Sarah Jacobsson Purewal/CNET

That unlimited data plan that you're fighting tooth and nail to keep -- is it really unlimited if your wireless carrier cuts back the speed once you exceed a certain data allotment?

Not really, no, but such an experience is far from uncommon. Last year, Verizon announced ( and then quickly rescinded) plans to throttle, or slow down, unlimited data users who went over 4.7GB per month. But does that mean that unlimited data users are free from throttling constraints? Not quite -- all of the major carriers throttle unlimited data users to some extent, although not necessarily constantly (T-Mobile likes to call it "prioritization"). Usually this throttling happens after you surpass between 3 and 7 gigabytes of data.

Want to find out just how much your wireless carrier is cutting back your plan? Here's how you can find out:

Step 1: Download Ookla's Speed Test app

Ookla's Speed Test app is free for iOS, Android, and Windows Phone.

Step 2: Run a few speed tests at the beginning of your billing cycle

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My data speed after using 0.014GB of my limited data plan. Sarah Jacobsson Purewal/CNET


In order to see how much your wireless carrier is actually throttling you, you'll need a baseline score. Use the Speed Test app to run a couple of tests from various locations at the beginning of your billing cycle, before you've exceeded your "limit."

Step 3: Run a few speed tests after you've exceeded your limit

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My data speed after using approximately 35GB on my unlimited plan. Sarah Jacobsson Purewal/CNET


Your "limit" will depend on your carrier and your plan, but for most users you should find that 5GB is around where your data goes slow. Try to run all of the speed tests in the same location and at the same time of day, to minimize any external factors that might affect data speed.

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It's a good idea to run multiple tests and take an average speed for accuracy. Sarah Jacobsson Purewal/CNET

Step 4: Conserve data

I know, I know -- the whole point of an unlimited plan is not having to conserve data. But, unfortunately, for "heavy" data users, throttling comes with the territory -- unless, of course, you pay full price for a limited plan with a high monthly allotment. Since most unlimited data plans are throttled at around 5GB, if you consistently need 10GB of high-speed data, a limited 10GB plan may actually be a better deal for you. Meanwhile, here are some surprising ways to lower your data usage.