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For AWS EC2, use On-Demand when usage is uncertain or short-lived; consider a Savings Plan when you can reliably commit to a steady hourly spend for one or three years; and compare EC2 Instance Savings Plans with Reserved Instances (RIs) when your workload is likely to stay within a particular instance family and Region. No option is universally cheapest: the right choice depends on how steady your usage is, how much flexibility you need, and whether you require capacity in a particular Availability Zone.
This comparison focuses on AWS EC2. AWS also offers Savings Plans for eligible database and SageMaker AI usage, but those plans cover different services and should be evaluated separately.
How the three AWS EC2 pricing options differ
| Decision | On-Demand | Savings Plans | EC2 Reserved Instances |
|---|---|---|---|
| What you commit to | No long-term commitment is described for EC2 On-Demand. AWS describes On-Demand Instances as billed by the second; check billing details for the specific service and usage. | A consistent dollar-per-hour usage amount for a one- or three-year term. | An instance configuration for a one- or three-year term. |
| Flexibility | Most flexible starting point for changing or uncertain usage. | Compute Savings Plans cover eligible EC2 usage across instance families and Regions, plus eligible Fargate and Lambda usage. EC2 Instance Savings Plans apply to a family in a Region, with changes to size, operating system, and tenancy allowed within that scope. | Discount applicability depends on the RI’s attributes. Regional and zonal RIs differ in Availability Zone flexibility and capacity reservation. |
| What happens if usage is lower than expected? | There is no term commitment to leave unused, though running usage still incurs charges. | The hourly commitment continues. Unused commitment can reduce realized savings; usage above the commitment is billed at On-Demand rates. | Charges apply for the full term regardless of actual use. |
| Does it reserve capacity? | No; capacity is a separate AWS choice. | No. AWS states, “Savings Plans does not provide a capacity reservation.” | A zonal RI provides a capacity reservation; a regional RI does not. |
| Useful comparison input | Actual hourly usage and forecast. | Cost Explorer recommendations, coverage, and utilization, checked against expected changes and existing commitments. | Expected use of the matching configuration and term, checked against current commitments. |
AWS’s EC2 purchasing-options guide, last updated June 22, 2026, frames these choices as pricing models with different commitment and flexibility trade-offs. An RI’s name can be misleading: “reserved” does not always mean capacity is held.
When should you use On-Demand instead of a Savings Plan?
Choose On-Demand when the workload is new, temporary, variable, or likely to change before a long-term commitment pays off. It lets you pay for running usage without committing to a one- or three-year baseline. That flexibility is useful while you measure a workload or when its future size, Region, or configuration is hard to predict.
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AWS recommends starting with On-Demand and analyzing usage before taking on a specific purchasing commitment. Track hourly consumption and separate durable baseline usage from spikes. If a workload has short peaks on top of a steady base, compare committing only to the reliable base and leaving excess usage On-Demand with committing to the peak.
When does a Savings Plan make sense?
A Savings Plan can suit a workload with a dependable hourly baseline when you want lower eligible rates but need flexibility across some usage changes. You commit to a dollar amount of usage per hour for one or three years. Eligible usage up to that commitment receives the plan’s rates; usage beyond it is billed at On-Demand rates. If eligible usage falls below the commitment, the unused portion can undermine the expected savings.
Choose between the two EC2 plan types
- Compute Savings Plan: Consider this when EC2 use may move between instance families or Regions, or when you also use eligible Fargate or Lambda. AWS says this plan can save up to 66% versus On-Demand, a published maximum rather than a forecast for your account.
- EC2 Instance Savings Plan: Consider this when usage is predictably within a single instance family and Region, while you may need flexibility to change size, operating system, or tenancy within that scope. AWS says this plan can save up to 72% versus On-Demand, also a maximum rather than a personalized estimate.
These are AWS’s published ceilings in its Savings Plans comparison documentation. The figures are not guaranteed realized savings and do not establish which option is cheapest for a specific instance, Region, payment choice, or workload.
When should you compare Reserved Instances with EC2 Instance Savings Plans?
Compare them when you expect usage to remain within a known EC2 configuration long enough to support a one- or three-year commitment. An EC2 Instance Savings Plan covers a family in a Region with some configuration flexibility. An RI’s discount eligibility depends on its attributes, so it may suit a well-matched, stable workload—but a narrow match can lose value if the workload changes or the RI goes unused.
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AWS’s EC2 comparison groups EC2 Instance Savings Plans and Standard RIs under a maximum savings figure of up to 72% versus On-Demand. That is an advertised ceiling, not a basis for choosing between them. Compare current terms, eligibility, projected utilization, and the value of flexibility using your account’s actual usage.
Do Reserved Instances guarantee capacity?
Only a zonal EC2 RI provides the capacity reservation described in AWS’s RI model. A regional EC2 RI can provide regional discount applicability without reserving capacity. Savings Plans do not reserve capacity, and On-Demand pricing alone is not a reservation.
If a workload must launch in a particular Availability Zone, treat capacity assurance as a separate requirement. AWS On-Demand Capacity Reservations are a separate mechanism; eligible Savings Plans or Regional RIs can discount them. An unused Capacity Reservation can still incur charges at On-Demand-equivalent rates, so capacity planning and pricing discounts should be assessed separately.
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- Define the workload boundary. Identify the AWS service, Region, instance family and configuration, operating system, tenancy, and whether capacity in a specific Availability Zone is required. This comparison covers EC2; database and SageMaker AI Savings Plans have distinct eligibility.
- Measure hourly usage. For a new or uncertain workload, begin with On-Demand and observe actual demand. Identify the stable baseline separately from spikes and seasonal or temporary usage.
- Match flexibility to likely changes. If the baseline is dependable but could shift among families, Regions, or eligible compute services, evaluate a Compute Savings Plan. If it should remain within one family and Region, compare an EC2 Instance Savings Plan with an RI that matches the expected configuration.
- Model a baseline commitment plus variable excess. Compare that approach with committing to the whole peak. Savings Plan usage over its hourly commitment is billed at On-Demand rates, so committing to volatile peaks can increase underuse risk.
- Review recommendations and existing commitments. AWS Cost Explorer recommendations use historical On-Demand usage and the selected plan type, term, and payment option. Treat the recommendation as an input, not a guarantee: test its assumptions against expected workload changes and existing Savings Plans or RIs. Benefits may be shared under consolidated billing depending on AWS settings.
- Check purchase terms before committing. AWS says Savings Plan terms cannot be changed after purchase except under narrowly defined return rules in its FAQ. RI charges apply through the term regardless of use. Confirm current terms in your account before purchase.
- Address capacity separately. If continuity depends on capacity in a particular Availability Zone, assess a zonal RI or a separate Capacity Reservation. A discount commitment by itself does not hold EC2 capacity.
AWS’s Savings Plans FAQ describes plan commitments, Cost Explorer recommendations, and capacity limitations. The AWS Well-Architected Framework guidance on pricing-model analysis also emphasizes matching commitment choices to usage and treating capacity reservations as a separate concern. For detailed RI behavior, AWS’s Reserved Instances and other reservation models whitepaper was published March 29, 2021; check current EC2 documentation and account terms for purchase specifics.
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What do the advertised savings figures mean?
“Up to” figures describe AWS’s published maximum comparisons with On-Demand, not an expected result for every customer. Realized savings depend on eligible usage, the plan or RI attributes, term, payment option, utilization, and current pricing. Base a decision on account-specific costs and the likelihood that committed usage will remain eligible—not on a headline ceiling alone.
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