Certain hosting products may have what is known as metric-based billing. This is a "pay-as-you-use" solution. This is commonly used on our reseller hosting. For example, each reseller hosting account includes a certain number of cPanel accounts. Instead of upgrading to the next package, metric-based billing charges you for the number of accounts you're over by. 

In this example, the reseller account includes 30 cPanel accounts, but the user is only using 21. If the user adds 9 more accounts, they will be at their reseller limit. But with metric-billing, if they add 10 more accounts, they will be billed an additional $1, assuming they do not add any additional accounts. If they add 13 more accounts, they'll be over by 4 accounts and will be charged an additional $4.

Current usage can be found at the bottom of your service page in the customer portal.

Metric billing is great for small overages, however if this customer were to suddenly jump to 100 cPanel accounts, it would make more financial sense to upgrade to the reseller plan that offers 100 cPanel accounts included.

Suspended accounts count towards your usage. If you notice that you're over your limit but you have suspended accounts that are no longer needed, delete them to reduce your usage.