Upgrades to your account are pro-rated to your next month billing cycle. This includes new servers, servers upgrades, overages and service upgrades.
This pro-rated upgrade amount will be billed at the time of the upgrade completion.
Example: If your billing date is the 11th of the month and you purchase a new server on the 20th. You will be billed a pro-rated amount of 20 days(20th to 30th + 1st to 10th =20 days) on the next billing date, you will be billed the full amount of the upgraded service.