Is a 100% uptime guarantee credible?

As marketing, common; as engineering, no — hardware fails and networks partition. A 100% claim means the provider is confident and willing to hand out credits, with the definitions section doing the heavy lifting. Judge providers by status-page history and incident communication instead.

How do I actually know my site's uptime?

Measure it yourself with external monitoring — services that request your site from several locations every minute and alert on failure. Provider dashboards report their platform, not your site; independent numbers are the ones worth quoting, and the alert is worth more than the statistic.

What are Uptime & SLA? — Getting Digital glossary

Uptime & SLA

Also: uptime guarantee, service level agreement, availability nines

Uptime measures the share of time a service is reachable, quoted in 'nines'; an SLA (service level agreement) is the contract clause that defines how that share is counted and what compensation — usually service credit — a miss triggers.

What the nines mean

Promise	Allowed downtime per year	Per month
99%	~3.7 days	~7.3 hours
99.9%	~8.8 hours	~44 minutes
99.95%	~4.4 hours	~22 minutes
99.99%	~53 minutes	~4.4 minutes

The arithmetic is the honest part. Everything else in an uptime promise lives in definitions: SLAs typically exclude scheduled maintenance, count only outages the provider's own monitoring confirms, start the clock after you file a ticket, and measure the platform's availability — not your site's, which also depends on your application, DNS and configuration. Read what is excluded before being impressed by the number.

The remedy clause deserves equal skepticism: a breached SLA usually yields a credit on next month's invoice — a proportional refund of hosting fees, not compensation for lost revenue. An SLA is best read as a signal of confidence and a definition of accountability, not as insurance. Real availability comes from architecture — redundancy, load balancing, tested recovery — and no contract clause substitutes for it.

Key takeaways

→Nines are exponential: 99% allows days of downtime a year, 99.99% under an hour — and each nine costs disproportionately more to deliver.
→An SLA defines counting rules and pays in service credit; it signals confidence but insures nothing — availability is built, not promised.

Related concepts

RelatedLoad Balancing
Availability targets are met by redundancy and balancing, not by contract clauses.

FAQ

Is a 100% uptime guarantee credible?: As marketing, common; as engineering, no — hardware fails and networks partition. A 100% claim means the provider is confident and willing to hand out credits, with the definitions section doing the heavy lifting. Judge providers by status-page history and incident communication instead.
How do I actually know my site's uptime?: Measure it yourself with external monitoring — services that request your site from several locations every minute and alert on failure. Provider dashboards report their platform, not your site; independent numbers are the ones worth quoting, and the alert is worth more than the statistic.