EC2 Spot vs On-Demand: the true cost difference in 2026

Quick Answer (TL;DR) EC2 Spot lists at up to 90% off On-Demand , but the effective savings after accounting for interruptions, engineering overhead, and workload retries land closer to 40 to 60% for most teams in 2026. Spot wins for stateless, retryable, or checkpointable workloads. It loses money on single-instance stateful services with strict SLAs. The honest formula: True savings = Spot discount × Utilization ÷ (1 + Interruption overhead) . Why the sticker discount is misleading The Spot price is a market price. AWS sets it against unused capacity in a given instance family, region, and Availability Zone, and it can move in minutes. The 90% headline is the maximum discount for a rarely-used instance family in an off-peak region. The workhorses ( m6i , c7i , r7g in us-east-1 ) usually sit at 55 to 75% off. Then there is the hidden cost of interruption. AWS gives a 2-minute warning before reclaiming a Spot instance. Handling that gracefully requires either a stateless workload, a checkpointed job, or careful autoscaler wiring. Teams that do not build for interruption end up with retries, half-finished batches, and engineering time that erases the savings. Fix #1: Diversify across instance types and AZs The single most effective way to reduce Spot interruption rate. Instead of asking for m6i.large specifically, ask for "any of m6i.large , m6a.large , m7i.large , m7a.large in any AZ." AWS pools capacity across the diversification pool. With Karpenter or Auto Scaling Groups: Set the NodePool or ASG's requirements to allow 5 to 15 instance types across families. Include both x86 and ARM (Graviton) options when your workload runs on both. Enable capacity-optimized-prioritized allocation strategy, which picks the deepest capacity pool at launch. Result: interruption rate drops from ~5% per instance-hour to under 1% on most workloads. Fix #2: Use Spot for the right workload shape Not every workload should be on Spot. The rule I use: Great fits : batch processing, data pi