What Is an SLA? Service Level Agreements Explained

An SLA (service level agreement) is a formal commitment between a service provider and its customers that defines the expected level of service — most commonly expressed as an uptime percentage. When a SaaS product promises 99.9% uptime in its SLA, it's saying the service will be available for all but roughly 43 minutes per month. If it falls short, the agreement typically specifies compensation: service credits, refunds, or extended subscriptions.

SLAs exist because "we'll try to stay up" isn't good enough for businesses that depend on a service. An e-commerce platform that goes down during a sale loses revenue. A payment processor that's intermittently unavailable breaks downstream transactions. The SLA puts a number on the commitment and attaches consequences to missing it.

What the numbers actually mean

The difference between uptime tiers looks small in percentages but large in minutes:

• 99% — 7 hours 18 minutes of downtime per month
• 99.9% — 43 minutes per month
• 99.99% — 4 minutes 21 seconds per month
• 99.999% — 26 seconds per month

Each additional nine roughly divides the allowable downtime by ten. Most web applications target 99.9% ("three nines"). Infrastructure providers like AWS and Google Cloud publish SLAs at 99.95% or 99.99% for individual services, though the effective uptime of a system that depends on multiple services is always lower than the weakest link.

SLAs and monitoring

An SLA without monitoring is a promise nobody can verify. To know whether you're meeting your uptime commitment, you need continuous checks from outside your infrastructure — your own servers can't reliably tell you they're unreachable. Uptime monitoring provides the measurement. SLA reports turn that measurement into evidence you can share with stakeholders or customers. When an incident does happen, incident management with timestamped updates creates the audit trail that shows how quickly the team responded.

Related terms: uptime, SLO, MTTR, incident management, status page