Why Your AWS Bill Tripled After Migration (and How to Fix It)

Written By Rohan Wiese
Updated on April 7th, 2026

Organizations migrate to AWS for reduced infrastructure costs and operational flexibility, yet post-migration, their bill turns out to be three times higher than expected.. Within 3 to 6 months of migration, AWS bills frequently exceed projections by 30 to 60%, leaving leadership questioning whether the migration delivered its promised benefits. This article explains the most common causes of AWS cost optimization after migration and provides clear, step-by-step fixes to bring your cloud spending back under control.

Table of Contents

Symptoms of a Bloated AWS Bill After Migration

Several warning signs indicate your AWS costs are running out of control after migration. There are some common indicators of AWS bill increased after migration:.

Your monthly AWS invoice is significantly higher than your previous on-premises infrastructure costs.
The EC2-Other line in AWS Billing has spiked without any visible increase in instance count.
NAT Gateway and cross-AZ data transfer charges have increased sharply without any configuration changes.
Dev and staging environments are running continuously, even outside business hours.
No resource tagging exists to attribute charges to a specific team, project, or workload.
Unattached EBS volumes, idle load balancers, and forgotten snapshots are quietly generating hourly charges.

What Causes the AWS Bill to Triple After Migration?

Now, first we will understand the root causes of AWS cost optimization after migration in order to fix them efficiently.

Most of the time, cost spikes in AWS pricing after lift and shift without any cloud-native optimisation.
Routing private subnet traffic through NAT gateways instead of VPC endpoints adds avoidable per-GB data processing charges.
Moreover, the process to run all workloads on On-Demand pricing instead of Savings Plans results in paying up to 66% more than necessary.
Orphaned resources such as unattached EBS volumes, unused Elastic IPs, and idle load balancers accumulate silent hourly charges.
Furthermore, public IPv4 address charges introduced in February 2024 inflate bills for workloads with multiple public-facing instances.

How to Fix Your AWS Bill After Migration

We will focus on the most effective fixes to reduce AWS cost optimization after migration.

Right-Size EC2 Instances Using Compute Optimizer
Switch to Savings Plans After Right-Sizing
Reduce NAT Gateway and Data Transfer Costs
Clean Up Orphaned and Idle Resources
Enable Cost Explorer and Set Budget Alerts

Read through each fix carefully and apply it based on the cause you identified above.

Fix 01: Right-Size EC2 Instances Using Compute Optimizer

Over-provisioned computers are the single reason why AWS bill is so high post-migration.. AWS Compute Optimizer analyzes CloudWatch utilization metrics and recommends the correct instance size for your actual workload.

Steps to Right-Size EC2 Instances

Firstly, open the AWS Management Console and navigate to Compute Optimizer.
After that, you need to enable Compute Optimizer for your account or organization.
In this step, you have to open the EC2 instances view and filter findings by Over-provisioned.
Next, open the EC2 instances view and filter findings by Over-provisioned.
Now, review each recommendation and note the suggested instance type and projected savings.
Furthermore, apply recommended instance types in a staging environment and run your performance tests.
Compute Optimizer incorporates on-demand pricing and discounted pricing through Savings Plans or Reserved Instances when calculating savings and ranking recommendations.
At last, apply approved changes to production and confirm application stability.

This is a critical step in AWS cost optimization after migration.

Fix 02: Switch to Savings Plans After Right-Sizing

Never commit to a savings plan before right-sizing. Once your true baseline compute need is established, you need to switch from On-Demand to a commitment model.

Steps to Purchase a Savings Plan

Firstly, you need to open AWS Cost Explorer >> Savings Plans >> Recommendations.
Thereafter, review the recommended hourly commitment based on your current usage patterns.
Next, choose between Compute Savings Plans for maximum flexibility or EC2 Instance Savings Plans for deeper discounts. The critical rule is not to commit to 100% of current usage if you have not yet optimised.
Now, select a one-year term, no-upfront-payment option to minimise financial risk initially.
At last, monitor savings plan utilisation monthly in Cost Explorer and adjust commitments as workloads evolve.

This step directly addresses the AWS bill increased after migration by reducing the cost significantly.

Fix 03: Reduce NAT Gateway and Data Transfer Costs

NAT gateway is the hidden reason behind the AWS billing issues after cloud migration.

Steps to Reduce NAT Gateway Costs

Firstly, open VPC Flow Logs and identify which resources send the highest volume of traffic through your NAT gateways.
After that, ensure that your AWS resources sending significant traffic are in the same Availability Zone as the NAT gateway, or create a NAT gateway in each Availability Zone with resources to avoid cross-AZ charges.
Next, create a gateway VPC endpoint and route all S3-bound traffic through it instead of the NAT gateway, as there are no data processing or hourly charges for using gateway VPC endpoints.
At last, you need to review the remaining NAT gateway traffic and evaluate AWS PrivateLink interface endpoints for other frequently accessed AWS services.

Note: If you need to migrate AWS WorkMail emails to Google Workspace, you can use the Aryson Email Migration Tool. Moreover, this software aims to maintain data integrity and security during the migration. Also, this utility provides the user with advanced features.

Conclusion

In the above article, we discussed the key root causes of post-migration AWS cost overruns, including lift-and-shift overprovisioning, NAT gateway and cross-AZ data transfer charges, on-demand pricing for steady workloads, orphaned resources, and new public IPv4 address fees. Along with that, we explored five targeted manual fixes: right-sizing with Compute Optimizer, switching to Savings Plans, replacing NAT gateways with VPC endpoints, cleaning up idle resources via Trusted Advisor, and establishing full cost visibility with Cost Explorer and Budget alerts. Therefore, apply the given fixes, and your AWS cost optimization after migration without any loss in application performance. Likewise, if you need further help in order to optimize your AWS environment, you can consult your cloud architect or AWS Support team for guidance.

FAQs

Q1. Why did my AWS bill triple after migration?

Ans: The most common causes are lift-and-shift over-provisioning, unexpected NAT gateway and cross-AZ data transfer fees, running all workloads on On-Demand pricing, orphaned EBS volumes, and a lack of cost monitoring or resource tagging.

Q2. What is the fastest way to reduce a post-migration AWS bill?

Ans: Enable AWS Compute Optimizer, filter for over-provisioned instances, right-size them, and then switch steady-state workloads to a Compute Savings Plan. These two steps alone can reduce compute spend significantly without impacting performance.

Q3. Are NAT Gateway charges a major contributor to post-migration cost spikes?

Ans: Yes. NAT gateway data processing fees, especially when combined with cross-AZ traffic, are among the most overlooked hidden costs after migration. Replacing NAT gateways with gateway VPC endpoints for S3 and DynamoDB eliminates those charges at no additional cost.

Q4. How can I monitor AWS costs to prevent future bill spikes?

Ans: Enable AWS Cost Explorer, configure AWS Budgets with threshold alerts, enforce resource tagging across all accounts, and review the Cost Optimization Hub dashboard weekly during the first three months after migration.

Q5. Is lift-and-shift always a bad migration strategy?

Ans: Lift-and-shift is a valid approach for speed, but it must be followed immediately by a post-migration optimization sprint. Leaving workloads in a lift-and-shift state long-term leads to compounding cost overruns and growing technical debt.

5/5 - (2 votes)

About The Author:

Rohan Wiese

Rohan Wiese is a Technical Content Writer at Aryson Technologies, specializing in databases, e-mail recovery, and e-mail migration solutions. He enjoys conducting research and generating information that assists database administrators, businesses, and novices in resolving issues with MS SQL Server, MySQL databases, Cloud Computing, and Microsoft Exchange.

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