"99.99% uptime" appears on nearly every enterprise quote. Most buyers nod at it and move on. It is worth ninety seconds of arithmetic, because it is one of the few numbers in the contract that is genuinely enforceable.
The maths
99.99% availability allows roughly 4.4 minutes of downtime per month. For comparison, 99.9% — one fewer nine — allows about 43 minutes. That is an order of magnitude difference hiding behind a single decimal place, and it is the difference between a blip nobody reports and an outage that reaches your leadership team.
What else is in the document
Uptime is the headline, but the SLA usually commits the carrier to more than that:
- Latency — a maximum round-trip time across the carrier's network.
- Packet delivery — typically 99.9%+ of packets delivered, which is what actually determines whether voice and video hold up.
- Mean time to repair — a defined window for restoring service, not a vague promise to look into it.
- Service credits — money back when the targets are missed.
The credits are rarely large enough to compensate for a bad outage. Their real function is to give the carrier a financial reason to care, and to give you a documented basis for escalation.
What it does not cover
Read the exclusions. Scheduled maintenance is almost always excluded, as is anything on your side of the demarcation point — your router, your firewall, your cabling. An SLA on the circuit does not protect you from a failure in your own equipment room.
Why best-effort broadband has none of this
Shared broadband carries no such obligations regardless of the speed on the box. That is the actual distinction between "business internet" tiers: not megabits, but whether anyone has contractually promised you anything.
The question to ask
When you receive a quote, ask for the SLA document itself rather than the number on the summary page. If it takes more than a day to produce, that tells you something about how the relationship will go.
