Why do sums of blended and unblended cost in a month differ in CUR?

Question

I have a full month of CUR data, using the following SQL:

```sql
SELECT sum("lineitem_blendedcost"), sum("lineitem_unblendedcost")
FROM "billc"
WHERE lineitem_productcode='AmazonRDS'
```

I expect the two sums to be the same as this is a whole month of data, blending should only apply at month level. However they differ from each other at about 1-2%.

The same is true for AmazonEC2.

Where does the gap come from? Thanks!

Vamsi Krishna · Answer

Ideally, it would not match. Unless, you are looking at the calculation of a single account (or) if you don't have consolidated billing set up, in addition to this if you don't use a reserved instance.

Like mentioned above, blended costs are calculated by multiplying each account’s service usage against something called a blended rate, that is an average rate of on-demand usage, as well as savings plans and reservation-related usage, that is consumed by member accounts in an organization for a particular service.  It is not usually a good filter to utilize.

AWS Support - Craig · Answer

Hi Zhang,

We'll need a bit more info to better assist. Our Support team will be able to take a closer look into this for you.

Be sure to reach out through the Support Center, here:

go.aws/support-center.

Regards,

\-Craig M.

sahniks · Answer

This can happen if the account is a part of an organization in AWS Organizations. Blended rates are the averaged rates of a given resource type used by all the member accounts in an organization in AWS Organizations. If the CUR is for just one account, the sums of blended and unblended cost may differ due to differences in pricing dimensions such as regions, instance types, storage classes, and the usage of Reserved Instances and Savings Plans between accounts.

Why do sums of blended and unblended cost in a month differ in CUR?

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