iTechGuides is reader-supported. When you buy through links on our site, we may earn an affiliate commission. As an Amazon Associate I earn from qualifying purchases. Learn more
An AWS Application Load Balancer (ALB) bill can rise for reasons other than data volume. The bill combines a charge for how long the load balancer runs with a usage charge measured in Load Balancer Capacity Units (LCUs). AWS calculates LCU use from four dimensions—new connections, active connections, processed bytes, and rule evaluations—and the highest normalized dimension sets the LCU consumption. Bandwidth matters, but it is only one part of the calculation.
What an ALB bill charges for
An ALB has two distinct charge components: load-balancer running time and LCU usage. AWS billing reports identify running-time usage with the code LoadBalancerUsage and LCU usage with LCUUsage. Reserved-capacity codes may also appear when reservations apply. The billing-code definitions are in AWS’s Elastic Load Balancing billing and usage report documentation.
That distinction matters when a bill seems disproportionate to traffic: the runtime charge is not calculated from bandwidth, and the variable LCU charge is not a byte-only meter. AWS describes LCU dimensions as averages over an hour, with the highest normalized usage determining the LCU amount for that hour.
How AWS determines LCU usage
AWS evaluates four dimensions. Each has its own per-LCU threshold, so raw bytes, connections, and rule counts cannot be compared directly. Compare each metric with its applicable threshold; the dimension that uses the greatest share of its threshold is the one that determines consumption.
#1 Best Overall
| Dimension | One LCU includes | What can make it matter |
|---|---|---|
| New connections | 25 new connections per second | A high rate of newly established connections, even if they are short-lived. |
| Active connections | 3,000 active connections per minute; 1,500 with mutual TLS | Many connections remaining open at once. |
| Processed bytes | 1 GB per hour for EC2 instances, containers, and IP targets; 0.4 GB per hour for Lambda targets | The data processed by the load balancer. This threshold varies by target type. |
| Rule evaluations | 1,000 rule evaluations per second | Requests evaluated against configured listener rules. The first 10 processed rules are free; if 10 or fewer rules are configured, AWS says this dimension is ignored. |
These thresholds and qualifications come from AWS’s ALB pricing page. Mutual TLS also changes the active-connection threshold, and its certificate metadata counts toward processed bytes. Certificate key sizes affect connection calculations for HTTPS listeners.
Why bandwidth alone can mislead
Processed bytes can be the largest LCU dimension, but that depends on the workload. AWS’s pricing page gives an illustrative example—not a general traffic benchmark—in which processed bytes account for 1.08 LCUs, compared with 0.04 for new connections, 0.04 for active connections, and 0.25 for rule evaluations. The example shows why bytes can dominate; it does not establish which dimension is driving any particular ALB’s bill.
Other traffic patterns can put a different dimension on top. Many short-lived connections can make new connections more significant; many simultaneous open connections can make active connections more significant; and a rule-heavy request path can make rule evaluations more significant. These are ways to interpret the pricing model, not a diagnosis of an account without its metrics.
How to find the source of your ALB charge
- Find the load balancer and billing period. In your AWS billing data, distinguish
LoadBalancerUsage(running time) fromLCUUsage(LCU consumption). Check for reserved-capacity codes if your account uses reservations. - Inspect the ALB’s CloudWatch metrics. Compare
ProcessedBytes,NewConnectionCount,ActiveConnectionCount, andRuleEvaluations. Also checkConsumedLCUs, which AWS says is always reported and reflects actual LCU consumption. Metric definitions are in AWS’s CloudWatch metrics documentation for Application Load Balancers. - Compare normalized usage, not unlike raw counts. Evaluate each dimension against the threshold that applies to your configuration. Confirm the target type, whether mutual TLS is enabled, and—where relevant—the certificate key size. These details can change the thresholds or calculations.
- Estimate future usage with your own inputs. Use the AWS Pricing Calculator with your actual Region and workload assumptions. Do not treat a sample from another Region as your rate.
Why an AWS pricing example may not match your bill
AWS’s pricing page illustrates an hourly ALB charge of $0.03114 in US East (N. Virginia), made up of a $0.0225 hourly charge and a $0.00864 LCU charge. These are the rates and workload assumptions in AWS’s published example, not universal or timeless prices. Region and configuration matter, so use the current pricing information and calculator for your own case.
The public pricing and metric documentation explain how to interpret the charge, but they cannot identify the driver of an individual account’s bill. To determine that, match the billing codes and period to the ALB’s CloudWatch metrics.
Quick Recap
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
