upgrade shinyapps.io and paying the difference


Will upgrading from a yearly subscription (e.g. BASIC) to a higher one (e.g. STANDARD) mean you'd only pay the difference?

I am not completely clear about this section of the user guide:
Upgrades take effect immediately, and if there is a prorated charge amount, it will be charged shortly after the upgrade. Any unused days or months in your current plan will automatically be credited against your new plan.