Legacy hyperscalers separated raw storage costs from data transfer and API requests. This unbundling destroys budget predictability, especially when startups begin scaling their infrastructure. Your actual cost depends entirely on how often applications read, write, and move data.

The mathematical reality of egress overages

Base object storage usually costs around $0.02 per GB. Internet egress on legacy hyperscalers runs about $0.09 per GB. This structural difference pushes true spend 2 to 5 times higher than the raw storage rates you see on their pricing pages.

If an application stores 10 TB but serves 50 TB to users, egress dominates the bill. High-frequency API calls compound the damage. A system executing 500,000,000 GET requests and 50,000,000 PUT requests adds hundreds of dollars in operational fees.

Calculation framework (your REAL cloud costs)

Step 1: calculate base storage and request volume

Multiply total stored GB by $0.02. Audit API logs to find total operations, then multiply total GET requests by $0.0004 per 1,000. Multiply PUT, LIST, and DELETE requests by $0.005 per 1,000.

Step 2: calculate internet egress and cross-region penalties

Identify total outbound data volume. Multiply the initial 10 TB by $0.09 per GB and the next 40 TB by $0.085 per GB. Add $0.01 per GB for data replicating across regions or moving between availability zones.

Step 3: calculate NAT gateway and load balancer surcharges

Map the data path. Add $0.045 per GB for NAT gateway processing and $0.008 per GB for load balancers. Add these figures to the totals from Step 1 and 2 to determine actual monthly spend.

Audit protocol for infrastructure teams calculating cloud costs

Run this calculation against the last 3 months of cloud billing logs. Track outbound bandwidth growth alongside total API request counts in your monitoring dashboard.

Set automated alerts at 15% above baseline traffic to isolate runaway transfer fees before invoice generation, no matter your provider.