Azure Reserved Instances vs Savings Plans: depth vs flexibility

Quick answer

Azure Reserved Instances commit to a specific VM size/region for up to ~72% off — deepest discount, least flexible. Azure savings plans commit to an hourly dollar spend for up to ~65% off and apply automatically across families and regions. Use RIs for a stable, unchanging fleet; savings plans for changing workloads. Both stack with Azure Hybrid Benefit, and you should commit to the baseline, not the peak.

Azure's two commitment models answer the same question — "pay less for compute you'll keep running" — with a classic trade between discount depth and flexibility. Picking right is mostly about how stable your fleet is over the commitment term.

Reserved Instances: deeper, rigid

An RI commits to a specific VM size in a specific region for 1 or 3 years, up to ~72% off pay-as-you-go. The catch is rigidity: resize the VM, move regions, or change families and the reservation may stop applying and sit idle (Azure allows some exchanges and cancellations, but it's friction). RIs reward a fleet you're confident won't change.

Savings plans: flexible, slightly less deep

An Azure savings plan for compute commits to an hourly dollar amount (say $5/hour) for 1 or 3 years, up to ~65% off, and applies automatically to whatever compute you run up to that amount — across VM families, sizes, and regions. Resize or re-architect and the discount follows your spend instead of stranding. You give up a few points of maximum discount for that freedom.

How to choose

Stable fleet, known sizes: Reserved Instances for the deepest discount.
Evolving workloads, frequent resizing, or mixed families: savings plans, so the commitment never strands.
Both: reserve the truly fixed core, cover the shifting remainder with a savings plan.

Stack with Hybrid Benefit, commit to baseline

Both stack with Azure Hybrid Benefit — bring your own Windows/SQL licenses on top of the commitment discount for the deepest total saving. And whichever you choose, commit to the baseline you reliably run 24/7, not the peak: let the variable top end run on-demand or on Spot VMs. Over-committing strands money on idle capacity. This mirrors the AWS decision in Reserved Instances vs Savings Plans.

FAQ

What's the difference between Azure Reserved Instances and Savings Plans?

Reserved Instances commit to a specific VM size in a region for 1 or 3 years at up to ~72% off, but they're rigid — change the size or region and the reservation may not apply. Azure savings plans for compute commit to an hourly dollar spend (e.g. $5/hour) for 1 or 3 years at up to ~65% off, and apply automatically across VM families, sizes, and regions.

Which saves more, RIs or savings plans?

Reserved Instances generally offer a deeper maximum discount (~72% vs ~65%) for a stable, unchanging workload. Savings plans trade a few points of discount for flexibility — they follow your compute spend wherever it moves. For a fixed fleet, RIs win on raw discount; for a changing one, savings plans win on not stranding the commitment.

Can I combine them with Azure Hybrid Benefit?

Yes. Azure Hybrid Benefit (bring your own Windows/SQL licenses) stacks on top of both reservations and savings plans. Combining a reservation with Hybrid Benefit on a Windows VM can reach the deepest total discount Azure offers.

What happens if my workload changes after I commit?

With an RI, if you resize or move the VM the reservation may no longer match and sits unused (though Azure allows some exchanges and refunds). A savings plan keeps applying as long as you have compute spend up to the committed hourly amount, so workload changes don't strand it. That flexibility is the main reason to pick a savings plan.

How do I decide how much to commit?

Commit to your steady baseline, not your peak. Look at the minimum compute you reliably run 24/7 and cover that with reservations or a savings plan; let the variable top end run on-demand or Spot. Over-committing strands money on capacity you don't use.

How does C3X help with commitment decisions?

C3X prices your VMs and compute resources at on-demand rates from your Terraform, giving you the baseline figure to size a reservation or savings plan against — so you commit to a number grounded in your actual fleet.

What to do next

A good commitment starts from a real baseline number. C3X prices your azurerm_linux_virtual_machine and other compute at on-demand rates from your Terraform, so you can size a reservation or savings plan against the fleet you actually run. The quickstart runs it in minutes.