T-Mobile‘s always been a bit vague when it comes to how it manages its unlimited 4G LTE Simple Choice plans. Now the carrier’s cleared up exactly when it will throttle (or “de-prioritize”) your connection.

Updates to the fine print on both the individual and family plans reveal that using more than 21GB of data per month will get you de-prioritized. That means T-Mobile slows down your service compared to other customers, though only at times when the demand for data is particularly high. Of course, 21GB is a lot of data, but if you have a big family or just tether a lot you could probably get there pretty fast.

Until recently, T-Mobile simply warned that customers who were in the top 3 percent when it came to data use would be throttled. At least now you know exactly when these penalties kick in. Still, T-Mobile hasn’t actually said how slow your speeds may drop, which would be a nice detail to know.