EC2 Idle & Rightsizing Calculator
Price idle and oversized EC2 capacity, then compare the three fixes: schedule it off, size it down, or commit. Counts the EBS volumes and Elastic IPs that keep billing after you stop an instance, the reason stopping saves less than expected.
The three fixes, priced
| Schedule it off outside needed hoursLeaves $160.00/mo still billing. EBS volumes, and any unattached Elastic IP | $2,035.20/mo |
| Rightsize to m5.largePeak CPU of 18.0% leaves room for one size down | $1,401.60/mo |
| Commit to a Savings PlanIndicative band, 1yr no-upfront to 3yr. Compute only, storage is never covered by a commitment. | $560.64 to $1,261.44/mo |
| Best single option | $2,035.20 |
What this model assumes
- Storage is charged in every scenario. Only the compute line responds to scheduling. This is the difference between this tool and the ones that quote a percentage of your whole bill.
- Rightsizing is offered one step at a time. Halving vCPU roughly doubles utilisation, so the recommendation only appears below 40.0% peak CPU. Tools that recommend downsizing at 60% peak are recommending an incident.
- Commitment discounts are a band, not a rate. The real figure depends on instance family, region and payment option, and AWS publishes a matrix rather than one number. A single confident percentage here would be wrong for most readers.
- Scheduling and committing are mutually exclusive in practice. A Savings Plan bought against hours you then switch off is wasted commitment. Pick the largest single option, not the sum.
Frequently asked questions
Do you get charged for a stopped EC2 instance?
Not for the instance hours, but yes for its storage. EBS volumes attached to a stopped instance bill at the full rate, so a stopped m5.xlarge with a 500 GiB volume still costs $40 a month. Worse, an Elastic IP costs nothing while attached to a RUNNING instance and $0.005 an hour once it is not, so stopping an instance can start a charge you did not previously have.
How much can I save by scheduling EC2 instances off?
A weekday 8am-8pm schedule runs about 260 hours instead of 730, so roughly 64% of the compute charge. That figure applies to compute only. Once storage is counted the real saving on a typical dev fleet is nearer 50%, and lower still for instances with large volumes.
Should I rightsize or buy a Savings Plan?
Rightsize first, then commit to what is left. A Savings Plan bought against capacity you later remove is wasted commitment you cannot cancel, and the same logic applies to scheduling, commitments cover hours, so committing to instances you plan to switch off is paying twice. This calculator deliberately shows the largest single option rather than a sum.
What CPU utilisation counts as an idle EC2 instance?
Below about 5% peak CPU an instance is doing essentially nothing and should be questioned rather than optimised. Below 40% peak there is usually room for one size down, but not more than one, because halving vCPU roughly doubles utilisation. CPU alone is not sufficient evidence: an instance can be memory-bound or network-bound at 5% CPU and still be busy.
Is it better to stop or terminate an idle EC2 instance?
Terminating releases the storage as well as the compute and is the only option that saves the whole cost. Stopping keeps the volumes, so it is the right choice for something you will genuinely restart and the wrong one for an instance nobody can name an owner for. If the peak CPU is near zero and nobody claims it, the answer is usually terminate.
Idle is easy to price and hard to find.
Finitizer profiles every instance against CPU, network and disk together, not CPU alone, so it distinguishes idle from memory-bound, and it tracks whether a commitment you already own still matches the fleet you actually run.