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HOME/Technical Articles/Amazon DocumentDB is finally discounted! Database Savings Plans offer significant cost savings

Amazon DocumentDB is finally discounted! Database Savings Plans offer significant cost savings

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With the recent announcement of "Database Savings Plans for AWS Databases" at AWS re:Invent 2025, Amazon DocumentDB is finally eligible for Savings Plans! This is a very welcome update for those who have felt that DocumentDB's discount options were weaker than those of Aurora, RDS, and other services. This was long-awaited and welcome news for us as well.
 
 
This article provides an overview of Database Savings Plans, an example of discounts using Amazon DocumentDB pricing examples from the official documentation, and a simple calculation based on a configuration assuming production use in the Tokyo region.
Please note that all prices in this article are estimates based on USD. For actual unit prices and exchange rates, please be sure to check the latest information on the official AWS pricing page.
 

What are Database Savings Plans?

First, let's explain Database Savings Plans, the main focus of this article. Simply put, Database Savings Plans are "savings plans specifically for database services." Like Compute Savings Plans, you commit to a fixed amount of usage (dollars/hour) for a year and receive a discount on on-demand rates. Its main features are as follows:
  • The contract period is one year (currently only one year is offered)
  • Committed usage is automatically discounted from on-demand pricing
  • The services covered are diverse, including Aurora, RDS, DynamoDB, ElastiCache, Amazon DocumentDB, Neptune, Keyspaces, Timestream, and DMS.
  • Applicable across instance families, sizes, regions, and database engines
  • Database RIs and DynamoDB reserved capacity cannot be stacked for the same usage.
According to the official explanation, the discount rate guidelines (upper limit) are as follows:
  • Serverless: Up to 35% off
  • Provisioned Instances (Aurora, RDS, DocumentDB, etc.): Up to 20% off
An important point about this update is that it includes Amazon DocumentDB instances and Amazon DocumentDB Serverless. This allows you to optimize costs while maintaining flexibility.
 

Amazon DocumentDB pricing model

Next, let's clarify the pricing structure for DocumentDB. Amazon DocumentDB (with MongoDB compatibility) pricing consists of four main components:
  1. On-Demand Instances
      • Cluster compute instances (instance class x number)
  1. Database I/O
      • Read and write I/O to storage volumes (in millions of I/O)
  1. Database Storage
      • Cluster Storage Volume Capacity (GB/month)
  1. Backup Storage
      • Backup usage exceeding data volume (GB/month)
In addition, you can choose from the following two storage configurations:
  • Standard (Pay-As-You-Go I/O Configuration)
    • Four-part billing: instance + storage + I/O + backup
    • This is a good option if I/O is likely to be less than 25% of the total cluster cost.
  • I/O-Optimized (I/O included configuration)
    • Charges are based on three items: instance, storage, and backup (I/O is free)
    • This is the way to go if I/O is likely to be more than 25% of the overall cluster cost
Database Savings Plans, the subject of this article, apply discounts to the price of "On-Demand Instances" (or DCUs for Serverless). It's important to note that discounts do not apply to storage or I/O fees.

Estimated price based on the official documentation (Standard configuration)

First, let's look at the cost savings of the Standard configuration, using a configuration similar to the example on the official AWS DocumentDB pricing page.
 
 

US East (N. Virginia) / db.r8g.large ×2

Example 1 (Standard configuration) in the official documentation uses an r5 instance, but we will perform calculations using an r8g instance so that it is eligible for Savings Plans.
  • Region: US East (N. Virginia)
  • Instance class: db.r8g.large
  • Number of instances: 2 (1 Primary + 1 Replica)
  • Storage: 50 GB
  • Backup storage: 50 GB
  • I/O: 200M (200 million) I/Os / month
The monthly costs for this configuration are as follows:
  • Instance cost: $0.304 x 730 hours x 2 = $443.84
  • Storage cost: 50 GB x $0.10 = $5.00
  • I/O cost: 200M × $0.20 = $40.00
Total: 443.84 + 5.00 + 40.00 = $488.84 / month

Image after applying Database Savings Plans

We will apply Database Savings Plans to this configuration and calculate the cost with a discount applied to the instance portion.
  • Instance cost (discounted): $0.243 x 730 hours x 2 = $354.78
  • Storage cost: $5.00 (unchanged)
  • I/O cost: $40.00 (unchanged)
Total: 354.78 + 5.00 + 40.00 = $399.78 / month
The reduction amounts and reduction rates in this case are as follows:
  • Savings: 488.84 USD - 399.78 USD = 89.06 USD / month
  • Reduction rate: about 18%
The savings amounted to approximately $89.06, which is approximately an 18% reduction for the entire cluster. We can see that the discount on the instance portion contributed significantly to the overall cost reduction.

Estimated based on Tokyo region / db.r8g.8xlarge x 3 configuration (I/O-Optimized configuration)

Next, we'll perform calculations based on more realistic production workloads. Here, we'll use an instance equipped with the latest Graviton4 processor and select the I/O-Optimized configuration, which has no I/O charges.

ap-northeast-1（Tokyo）/ db.r8g.8xlarge ×3

  • Region: ap-northeast-1 (Tokyo)
  • Instance class: db.r8g.8xlarge
  • Number of instances: 3 (1 Primary + 2 Replica)
  • Storage: 1 TB
  • Backup storage: 1 TB
The monthly costs for this configuration are as follows:
  • Instance cost: $5.863 x 730 hours x 3 = $12,839.97
  • Storage cost: 1,000 GB x $0.30 = $300.00
  • Backup cost: 1,000 GB x $0.02 = $20.00
Total: 12,839.97 + 300 + 20 = 13,159.97 USD / month

Monthly fee when Database Savings Plans are applied

Next, calculate the cost after applying Database Savings Plans. Discounts are applied to the instance portion only.
  • Instance cost (discounted): $4.690 x 730 hours x 3 = $10,271.1
  • Storage cost: $300.00 (unchanged)
  • Backup cost: $20.00 (unchanged)
Total: 10,271.10 + 300 + 20 = 10,591.10 USD / month
The reduction amounts and reduction rates in this case are as follows:
  • Savings: 13,159.97 USD - 10,591.10 USD = 2,568.87 USD / month
  • Reduction rate: approx. 19.5%
In the I/O-Optimized configuration, the instance price is set higher in exchange for not incurring I/O charges. As a result, the instance fee accounts for a much higher proportion of the overall cluster cost. As a result, the 20% discount on the instance portion is almost directly reflected in the overall cluster cost, resulting in a significant savings of approximately 19.5%.
As you can see, the I/O-Optimized configuration and Database Savings Plans are a great combination.

Steps to consider when introducing Database Savings Plans

When considering purchasing Database Savings Plans that include DocumentDB, we recommend following the steps below.
  1. Understand your on-demand costs For existing clusters, tally up your DocumentDB on-demand usage costs using Cost Explorer or your bill. For new deployments, create an estimate using the AWS Pricing Calculator.
  1. Determine the scope of coverage Consider whether you want to apply Savings Plans to not only DocumentDB but also other database services, such as Aurora, RDS, ElastiCache, and DynamoDB. Database Savings Plans can be applied across engines and regions, providing flexibility for potential database migrations or configuration changes in the future.
  1. Check the recommended values Check the "Savings Plans Recommendations" in the AWS Billing and Cost Management console. Based on your past usage, you'll be presented with a suggested optimal commitment amount ($/hour).
  1. How to Use Reserved Instances (RIs) It's effective to use them according to the characteristics of your workloads, such as applying highly discounted RIs to RDS, which you plan to continue using without changing the configuration for the next three years, and applying flexible Savings Plans to DocumentDB or Aurora, which you may be migrating or changing the configuration in the future.

summary

With the announcement of Database Savings Plans at re:Invent 2025, Amazon DocumentDB can now also benefit from Savings Plans.
In DocumentDB's pricing structure, the discount provided by Savings Plans applies to the instance portion (or DCUs for Serverless). In the case of the Standard configuration, you can expect an overall reduction of approximately 18%, while in the case of the I/O-Optimized configuration, which has a higher proportion of instance costs, you can expect an overall reduction of nearly 20%.
In particular, the flexibility to apply it across regions, instance families, and database engines is a major benefit in rapidly changing system environments. We encourage you to consider adopting it after taking into account your current costs and the likelihood of future configuration changes.
 
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