Why Cloud Cost Comparisons Are Harder Than They Look
On the surface, comparing cloud costs seems straightforward — look up the price per vCPU-hour, multiply by your instance count, and compare the total. In practice this approach misses most of the actual cost. Network egress, storage I/O, managed service premiums, support contracts, and the hidden costs of cloud operations routinely double or triple the apparent compute price.
This calculator focuses on the compute and storage layer — the most predictable part of your cloud bill. The real cost comparison between cloud providers and between public cloud and private infrastructure requires understanding all the cost categories that appear in a real bill, not just headline instance pricing.
The five cost layers
Compute
Instance pricing by vCPU and RAM. Varies by generation, commitment type (on-demand vs reserved vs spot), and geographic region. On-demand pricing is the published rate — reserved instances (1 or 3 year commitments) typically cut compute costs by 30–60%.
Storage
Block storage (EBS, Azure Disk, GCP Persistent Disk) is billed per GB-month regardless of utilization. Object storage (S3, Blob, GCS) is billed per GB stored plus per-request fees. Storage costs often exceed compute costs for data-heavy workloads.
Network egress
Data transferred out of a cloud region to the internet or to other regions is charged per GB — typically $0.08–0.09/GB for the first 10TB/month. Inbound data is free. High-bandwidth applications like video delivery, large file transfers, or data replication between clouds can generate egress bills that dwarf compute costs.
Managed services
RDS, Cloud SQL, ElastiCache, and similar managed services carry a 40–100% premium over self-managed equivalents running on equivalent compute. The convenience is real, but so is the cost. Many organizations find managed databases are their single largest cloud line item.
Support and operations
Enterprise support contracts add 3–10% of monthly spend. Cloud operations staff, tooling subscriptions, and training costs don't appear on the cloud bill but are real costs of running in public cloud. Private cloud adds capital expenditure and hardware operations staff on the other side of the ledger.
Hidden multipliers
License bring-your-own complexity, data transfer between availability zones ($0.01/GB on AWS), API request charges, NAT gateway fees, load balancer hours, and CloudWatch/monitoring costs collectively add 15–25% to most bills beyond the obvious compute and storage line items.
AWS vs Azure vs GCP — Key Pricing Differences
The three major cloud providers have converged significantly on compute pricing for standard general-purpose instances. Meaningful differences exist in storage pricing, egress rates, committed use discounts, and the pricing of higher-end instance families.
| Factor | AWS | Azure | GCP |
|---|
| Committed pricing model |
Reserved Instances — 1 or 3 year commitments with upfront payment options. Savings Plans offer more flexibility across instance families. |
Reserved VM Instances — 1 or 3 year terms. Azure Hybrid Benefit lets you apply Windows Server and SQL Server licenses to reduce costs further. |
Committed Use Discounts — resource-based (specific machine type) or spend-based. Applied automatically, no upfront payment required. |
| Automatic discounts |
None for on-demand. Spot instances for interruptible workloads. |
None for on-demand. Spot VMs for interruptible workloads. |
Sustained use discounts apply automatically when instances run more than 25% of a month — up to 30% discount with no commitment required. |
| Storage pricing |
EBS gp3 is cost-effective. Higher IOPS and throughput provisioned separately at additional cost. S3 is the reference standard for object storage pricing. |
Premium SSD v2 offers granular IOPS and throughput provisioning. Azure Blob storage costs slightly below S3 for equivalent durability. |
Persistent Disk pricing competitive with EBS. Extreme Persistent Disk for highest IOPS requirements. Cloud Storage (object) pricing competitive. |
| Egress pricing |
$0.09/GB first 10TB, declining tiers. Inter-region transfer charged both directions. |
$0.087/GB first 10TB. Zone-to-zone transfer within a region is free, unlike AWS. |
$0.08/GB first TB, $0.06/GB 1–10TB. Generally most favorable egress pricing of the three. Inter-region transfer pricing competitive. |
| Free tier |
12-month free tier for new accounts covers t2/t3.micro, 5GB S3, and many services. |
12-month free tier with $200 credit for new accounts. Ongoing free services for some products. |
$300 credit for 90 days for new accounts. Always-free tier includes e2-micro instance, 30GB standard disk, and other services. |
Private Cloud vs Public Cloud — The Real Economics
The decision between public cloud and private infrastructure is rarely as simple as comparing per-hour instance prices. Organizations that have run both carefully typically find that the economics depend heavily on utilization rate, workload stability, and organizational maturity around infrastructure operations.
When private cloud wins
Private cloud tends to deliver better economics when workloads are stable and predictable (high utilization rate justifies capital investment), when data sovereignty or regulatory requirements mandate on-premises control, when the organization already has data center infrastructure and operations staff, and when workloads are large enough that the capital cost amortizes favorably against public cloud on-demand pricing.
The break-even point varies by organization but frequently falls around 60–70% average utilization. Below that threshold, paying for idle public cloud capacity on-demand is typically cheaper than owning hardware. Above that threshold, the economics of owned infrastructure — particularly with OpenStack providing cloud-like automation — tend to favor private deployment.
When public cloud wins
Public cloud economics are strongest for variable or unpredictable workloads, new applications without established resource requirements, organizations without data center expertise or existing infrastructure, and workloads requiring geographic distribution across many regions. The ability to provision capacity in minutes without capital commitment has genuine economic value for workloads that cannot predict their resource needs months in advance.
Frequently Asked Questions
How accurate are cloud cost estimates from calculators?
Compute estimates from calculators are reasonably accurate for simple workloads — typically within 10–15% of actual bills for pure compute. The accuracy decreases as workload complexity increases. Egress costs, inter-service transfer fees, managed service premiums, and per-request charges are difficult to estimate without actual traffic data. Use calculator outputs as directional guidance for initial comparisons, then validate against actual bills or provider cost estimation tools (AWS Pricing Calculator, Azure Pricing Calculator, GCP Pricing Calculator) for final decisions.
Are Reserved Instances always worth it?
Reserved Instances and committed use contracts make financial sense when you have high confidence that the workload will run continuously for the commitment period. The math is straightforward: a 1-year reserved instance at 40% discount breaks even with on-demand at roughly 60% utilization — if the instance runs more than 60% of the time over the year, reserved pricing wins. The risk is commitment lock-in — if workload requirements change and the instance is no longer needed, you continue paying for unused capacity. AWS Savings Plans reduce this risk by allowing flexibility across instance families and sizes.
What is the real cost of cloud egress and why does it matter?
Egress fees — charges for data leaving a cloud region — have attracted significant regulatory attention and industry criticism because they create artificial switching costs and can be surprisingly expensive for data-intensive applications. At $0.08–0.09/GB, transferring 1 petabyte of data out of a cloud region costs $80,000–90,000. Applications that sync data between cloud and on-premises, serve large media files, or operate across multiple cloud regions can accumulate egress bills that exceed their compute costs. The European Union's Data Act and similar regulations have begun requiring providers to eliminate egress fees for customers switching providers, but these rules are still being implemented.
How do I reduce my cloud bill without migrating to a different provider?
The most impactful cost reduction measures within a single provider, roughly in order of impact: convert on-demand instances to Reserved Instances or Savings Plans for stable workloads (30–60% savings on compute); right-size instances by analyzing CPU and memory utilization and downsizing overprovisioned instances; delete unattached EBS volumes and unused snapshots which continue billing after instances are terminated; use S3 lifecycle policies to move infrequently-accessed objects to cheaper storage tiers; enable spot or preemptible instances for fault-tolerant batch workloads; and set up billing alerts to catch unexpected spend increases immediately rather than at month end.