Why is my Data exports cost and Cost Explorer cost not the same?

Question

When I add up the 'line_item_net_unblended_cost', 'reservation_net_effective_cost' and the 'savings_plan_net_savings_plan_effective_cost' fields from my Athena table I have created from the Data Exports object in my S3 bucket, the sum is around $100 lesser than what is being shown on the Cost Explorer tab [for one month]. I am storing it in CSV format then casting  the cost fields as double later.
The Data Export is in CUR 2.0 format
[The rest of the cost fields are 0.0]

re:Post Agent · Answer

There are several reasons why you might see discrepancies between the costs shown in your Data exports (Cost and Usage Reports) and those displayed in Cost Explorer:

1. Rounding differences: The billing features may round cost data in different ways, leading to small variations in the total amounts.

2. Data refresh settings: Cost Explorer automatically reflects refunds, credits, or Support fees applied after a bill is finalized. If you haven't activated automatic refresh for your Cost and Usage Reports, this could cause a mismatch.

3. Grouping of charges: Different billing features may group charges in various ways. For example, data transfer charges might be shown separately in one view but included within each service in another.

4. Timing of data updates: There might be slight differences in when each system updates its data.

5. Filtering and calculation methods: Ensure that you're applying the same filters and calculation methods in both systems. For instance, check if you're including or excluding the same types of charges, such as credits, in both your Athena query and Cost Explorer view.

6. CSV format limitations: Storing data in CSV format and then casting to double might introduce some precision issues, especially with very small amounts.

7. Aggregation levels: Make sure you're comparing data at the same level of aggregation (e.g., daily vs. monthly) in both systems.

If after checking these factors you still see a significant discrepancy, it would be advisable to open a support case with AWS. Provide them with the specific report name and billing period you're analyzing, so they can review your cost data in detail.

Remember that small differences are not uncommon due to the complexity of AWS billing across various services and pricing models. However, a difference of $100 for a month might warrant further investigation.  
**Sources**  
[Troubleshooting Cost and Usage Reports - AWS Data Exports](https://docs.aws.amazon.com/cur/latest/userguide/troubleshooting-cur.html)  
[Troubleshooting Cost and Usage Reports - AWS Data Exports](https://docs.aws.amazon.com/cur/latest/userguide/troubleshooting.html)

Why is my Data exports cost and Cost Explorer cost not the same?

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