AWS RDS free tier: Is free usage reset every month?

Question

I'm using AWS RDS by free tier.

I created a database in January, and created another databse in February.

Today morning, I got a message that I was charged 12 dollars for overusage.

I checked my AWS cost management, and found out that the cost for March so far is $0.

I know that the free tier gives me 750 hours.

But does it mean that I can use 750 hours every month?

If so, can I use one database for free every month because 750/24 = 31?

And did I get charged because I am activating two databases?

Thanks.

Answer 1

From the AWS documentation:

750 hours of Amazon RDS Single-AZ db.t2.micro Instance usage running MySQL, MariaDB, PostgreSQL, Oracle BYOL or SQL Server (running SQL Server Express Edition) – enough hours to run a DB Instance continuously each month

so if you run two instances, that will be a total of 1500 hours of usage, so you will be charged extra. But you can run one instance for free each month. Note that the RDS instance is part of the 12 months free tier in AWS. That means that this offer only holds for 12 months after creation of your AWS account.