Uptime guarantees are among the least useful numbers in hosting marketing, because the arithmetic is more forgiving than it sounds and the payout is usually trivial.
The arithmetic
- 99.9% allows around 43 minutes of downtime per month.
- 99.95% allows around 21 minutes.
- 99.99% allows around 4 minutes.
Most guarantees also exclude scheduled maintenance, problems caused by your own code, and network issues outside the provider's own equipment — which covers a surprising share of real outages.
What the SLA actually pays
Typically a credit against future service, pro-rated to the downtime. On a $10 plan, an hour of downtime is worth a few cents. The guarantee is a statement of intent, not insurance.
Better questions to ask
- Is there a public status page with real incident history?
- How quickly is a support ticket answered by someone who can actually act?
- How often are backups taken, and can you restore them yourself?
- How is scheduled maintenance communicated, and how far in advance?
A provider that publishes its incidents honestly is worth more than one advertising an extra nine.