We pro-rate all upgrades. Pro-rating means that we will apply any remaining funds you have on your current account towards the purchase of additional space.
For example, if you have a 1000GB annual plan that was purchased four months ago, you have paid $10.75 per month (129 / 12 = $10.75) or $43 in total ($10.75 x 4 = $43).
If you then decide to upgrade to a 5TB annual plan, we will now calculate how much money you have unused on your current account and credit it towards your new purchase. In this example, you have used $43 which means you have $86 remaining in credit ($129 - $43 = $86).
We now subtract your credit from your purchase of the 5TB annual plan. The $279 minus your remaining credit of $86 is $193, which is what you will be billed to upgrade this account.
In some cases our billing system will not immediately bill you for an upgrade, but will apply the price difference (as described above) to your next bill. If you ever have any concerns about how pro-rating will be applied (or has been applied) to your account, please be sure to reach out to our support team here.