What an SLA Actually Guarantees (and What It Doesn't)
99.9% uptime sounds like a high bar. It allows 8.7 hours of downtime per year — before the exclusions kick in. Here's what SLA numbers actually mean and how credits are capped to cover almost nothing.
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99.9% uptime. That's the number most vendors put in an SLA and most buyers accept without doing the math. It means 8.7 hours of allowed downtime per year. And that's before the exclusions — scheduled maintenance, force majeure, and customer-caused incidents typically don't count toward the number at all. Here's what uptime tiers actually mean for your business.
Three uptime tiers, three very different realities. 99% allows 87.6 hours per year — that's nearly four full days your service can be down and the vendor is still compliant. 99.9% is 8.76 hours. Better, but still a full business day. 99.99% is 52 minutes — that's the standard serious SaaS products hold themselves to, and it requires hot failover infrastructure to maintain.
The uptime number is only part of it. The exclusion clauses define what doesn't count against the SLA — and that's where most of the wiggle room lives. Scheduled maintenance windows, force majeure, incidents caused by the customer's own configuration, third-party service failures — all typically excluded. And when you do qualify for a credit, it's usually capped at one month's fees. If your downtime costs you $200,000, a $3,000 credit covers nothing.