AWS Savings Plans are financial mechanisms used to reduce your AWS bill by offsetting the cost of compute usage. Savings plans are similar to Reserved Instances in that they both discount your AWS bill based on expected AWS compute usage. Like a Reserved Instance, a Savings Plan represents a commitment to an amount of AWS usage over a one- to three-year period, but at a discounted price.
How Savings Plan Charges Appear in AWS Billing
Savings plans are represented in your AWS bill in three different ways. First, the savings plan line item which represents the amortized cost of the savings plan that you have purchased. Second, you will see credits applied to your bill as a result of the savings plan. Lastly, you'll see the additional field SavingsPlanEffectiveCost for each item. Read this section to see how those items are calculated.
The Savings Plan Line Item
A Savings Plan will come through to your bill as a Savings Plan line item. This line item will be the cost of your Savings Plan. As we know the cost of a savings plan is the financial commitment over the period that you purchased the plan. If you purchased a Savings Plan over a year period you would see the cost of this purchase amortized over the year. These charges are reflected in your bill daily (this only applies to Savings Plans that are purchased with no upfront cost).
To see your Savings Plan costs, open the Data page in Stax and filter the kind field to show records of type savings_plan. This will filter the data to only show your savings plan charges for the given month. By default, when searching over multiple months, results are aggregated across all months. Group by Interval to show charges aggregated by month.
The Credits Line Item
A Savings Plan is a commitment to an amount of compute usage over a period of time. Any "savings" created from purchasing a Savings Plan are applied through the mechanism of a credit for the savings plan discount. The credit applied to your account will be the daily value of the applied Savings Plan discount. This means two things:
- On your bill you are charged for EC2 instance usage and then credited the amount that is covered under your Savings Plan.
- The credit can be zero if you are not using any compute that is covered by your Savings Plan.
To see the credits that you are receiving from your Savings Plan discount go to the data page and add a filter to the "Usage code" field of savings_plan_discount. This will filter the data to only show you the Savings Plan discount credits applied to your account.
The Savings Plan Effective Cost
The Savings Plan effective cost is how AWS represents how these savings plan discounts are applied on an instance level. This means that for an EC2 instance you have the unblended cost (the cost without any discounts applied) and the savings plan effective cost. The Savings Plan effective cost is the cost of an instance with the hourly discount price applied to it. This distinction is important to see the true reflection of how your Savings Plan impacts your instance costs.
It is important to note that in usage mode, Stax will use the Savings Plan's effective cost, so that you see a true reflection of your instance "usage".
In the below example you can see that later in the month, charges for the Savings Plan start being applied. At this point you'll be begin to be charged the amortized cost of your Savings Plan (this charge occurs whether you are using your Savings Plan or not).
On a specific day, the charges for the EC2 instance spend may break down as follows:
- You're being charged for the Savings Plan you purchased.
- A portion of your EC2 spend is covered by your Savings Plan and thus receive the discount of the Savings Plan (this can range from 66% to 75% depending on the plan). It's important to remember that EC2 spend does not equate to EC2 instances.
- You're given a credit (a negative charge) for the instance spend that is covered by the Savings Plan. This is your "Savings Plan discount".
- Any EC2 spend not covered by your Savings Plan is charged at the standard on-demand rate. This can be the remaining (25%-33%) or additional EC2 spend beyond what is covered.