If your new plan has a different billing frequency
For example, switching from monthly to yearly, or free to paid. Your new plan's first full period begins immediately, and you're charged for that period minus any existing prorated account balance.
If your new plan has the same billing frequency
We keep your billing schedule the same and handle the change like this:
We immediately create a credit for the remaining portion of your current billing period.
At your next scheduled billing, you're charged the full amount for the upcoming period, minus your account balance (if any).
If your account balance is larger than the amount due, you won't be charged, and the remaining balance carries over to future periods until it's used up. If your balance doesn't cover the next period, your card is charged the difference.
Example: say you're on a monthly plan and switch with 15 days left in your billing period. We immediately credit the unused portion of your current plan to your account balance. At your next billing date, you're charged the new plan's full monthly price minus that credit. If the credit is larger than the charge, you pay nothing that month and the leftover rolls over to future months.
To switch plans, see How do I change my subscription.