On May the 3rd, I received this email from AWS:
This slightly concerned me as this was a direct charge to my card rather than my credit.
My first response was to go to the AWS Billing page and determine the reason for this charge. The Billing dashboard showed an amount $0.64 expenditure had occurred, and I, being unsure as to what this charge specified, checked my credits to determine whether the amount had been removed from there.
My credit page showed a fee charge similar to what I had calculated in my spreadsheet, of $16.17 USD credits.
This boosted my confidence in understanding my credit usage and fees, but didn’t resolve the reason why my card was being charged.
The next response was to click on the graph which showed my expenditure, and see if that helped. This lead me to the Cost Explorer option in the Billing Console, and showed me this information:
From this, I can see that Budget and Tax appear to make up the bulk of the costs.
By refining the Time range, I was able to preview my costs more clearly:
This one clearly shows that the Budget Service cost me $0.56 and Tax was $0.08, which comes to $0.64 total., which equals the amount that I was directly charged.
My conclusion from this is that not every service is charged to my credit, and that although the budgets are fantastic for warning me of my credit expenditure, I should keep in mind that they also come with a cost.