What is a spot or preemptible instance?

Spot instances (AWS) and preemptible VMs (GCP) are spare cloud capacity sold at a deep discount — typically 60–90% below on-demand prices. The trade-off is that the cloud provider can reclaim them with short notice, so they suit fault-tolerant, interruptible workloads.

Where do I find the spot discount percentage?

AWS publishes real-time spot prices at aws.amazon.com/ec2/spot/instance-advisor. GCP lists preemptible discounts on its pricing pages (usually a fixed 80% discount). Azure Spot prices vary by region and SKU.

What does the interruption buffer do?

When a spot instance is reclaimed, any in-progress work is lost and you may need to restart it. The interruption buffer adds a percentage to your effective cost to model this lost compute time. Set it to 0 if your jobs checkpoint frequently.

Does this cover data transfer or storage costs?

No. This calculator covers compute cost only. Data egress, EBS/persistent-disk storage, and network costs are billed separately by your cloud provider.

Can I compare on-demand vs reserved vs spot here?

Enter the reserved instance hourly price as your "on-demand price" in a separate row to see spot savings over reserved. Reserved discounts are typically 30–60%, so spot still wins for interruptible workloads.

Spot Savings Calculator

Name: Spot Savings Calculator
Availability: InStock
Author: Nham Vu

Enter your on-demand price, spot discount, and usage hours to see how much you save with spot or preemptible instances.

Instance configuration

On-demand hourly price (USD)

e.g. t3.medium on-demand = $0.0416/hr, m5.xlarge = $0.192/hr

Spot / preemptible discount 70%

1% 99%

Number of instances

Hours per month

730 = full month, 160 = business hours only

Interruption overhead 5%

0% 50%

Extra cost to account for restarted work after eviction

Monthly on-demand

—

Monthly spot cost

—

Monthly savings

—

Annual savings

—

Cost breakdown

Item	Per instance/mo	Total/mo

Fill in the inputs and click Calculate savings.

Summary

Enter your on-demand price, spot discount, and usage hours to see how much you save with spot or preemptible instances.

How it works

Enter the on-demand hourly price for your instance type.
Set the spot or preemptible discount percentage (typically 60–90% off).
Input the number of instances and hours per month you plan to run.
Optionally add an interruption buffer to account for spot terminations.
The calculator outputs monthly and annual savings with a cost breakdown.

Use cases

Estimate savings before migrating batch workloads to EC2 Spot or GCP Preemptible.
Compare spot vs reserved vs on-demand total cost for a given workload.
Justify spot adoption to finance teams with concrete dollar figures.
Evaluate multiple instance configurations side by side.
Factor in interruption overhead to get a realistic savings estimate.
Plan annual cloud budgets with spot pricing assumptions.

Frequently Asked Questions

Last updated: 2026-07-22 · Reviewed by Nham Vu