There's a default email notification that goes out when you reach 80% of the monthly limit, so you will know in advance if you need to make arrangements. Just double check on the account page that it's on: https://cluelabs.com/account/profile

If you do get close to the limit, you can just upgrade to the next service plan. If the new payment is higher - the system will upgrade you immediately and will just apply the unused credit to the new payment. And you can always shoot us a message to make changes manually.