Yes, 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.