You only pay for compute and storage that you’ve used. We calculate usage per day.
For example, if you set your app to 1 GB of RAM on day one, then scale down to 512MB of RAM on day two, you will pay less on day two.
If you have your app turned off for half of the month, then you will only pay for half of the month.
The cost estimate on creation and in the scale tab are estimates assuming you will have your app turned on with those specs for a full month.