Uptime SLAs Decoded: Advertised vs Measured, and What "Nines" Really Cost — 2026

"99.9% uptime" sounds like a rounding error from perfect. It's nearly 9 hours of downtime a year. This decodes what the nines actually mean — and compares advertised SLAs with independently measured uptime for hosting and business phone providers.

An uptime SLA is a promise; measured uptime is the reality; and the gap between "99.9%" and "99.99%" is an order of magnitude in downtime. This page does two things: translates the nines into real downtime per year, and compares what providers advertise with what reviewers measured.

Free to cite and link. Measured figures are from third-party monitoring at a point in time and vary; confirm current uptime and the SLA's credit terms before relying on them.

What the "nines" actually mean (downtime per year)

SLA"Nines"Max downtime / yearMax downtime / month
99.9%three nines~8h 46m~43m 50s
99.99%four nines~52m 36s~4m 23s
99.999%five nines~5m 15s~26s
100% SLA—0 (contractual; credits on any downtime)0

Standard arithmetic on a 365-day year: each extra "nine" cuts allowed downtime ~10×. A "100% SLA" is a credit commitment, not a physics guarantee.

Advertised SLA vs independently measured (hosting & UCaaS)

ProviderCategoryAdvertised SLAMeasured / notable
PressableManaged WP100% SLA, multi-region auto failoverFailover included at no extra cost
Liquid WebHosting100% SLA on VPS/dedicated (10× credit)Managed WP/Woo runs on Nexcess (99.99% guarantee)
NexcessManaged WP99.99% guarantee—
KinstaManaged WP99.99% SLAConfirmed delivered in April 2026 spot-check
SiteGroundHosting99.99% (cloud)~100% during monitoring
HostingerHosting99.9% SLA~99.94–99.98% measured over 12 months
BluehostHosting—99.97% over a 365-day benchmark (~2h21m total)
CloudwaysHosting—~99.98–99.99% over a 6-month test
GreenGeeksHosting99.9% guarantee~99.98% measured
GoDaddyHosting99.9% guaranteeOften exceeds it (100% in recent tests)
HostGatorHosting99.9% guarantee~99.89% measured (below the SLA)
A2 HostingHosting—Reviewers flag below-average uptime, frequent status-page interruptions
NextivaBusiness VoIP99.999% SLA (~5 min/yr)—
8x8Business VoIP99.999% SLA, sub-30s failover—

Key findings

  1. "99.9%" is ~9 hours of downtime a year — not a rounding error. The jump to 99.99% (four nines, ~53 min/yr) is a 10× improvement, and 99.999% (~5 min/yr) another 10×. When a host advertises "99.9%," read it as "up to ~9 hours down per year," and price the upgrade accordingly.
  2. Most hosts measure at or above their SLA — but not all. Hostinger (~99.94–99.98% vs 99.9% SLA), SiteGround (~100%), GreenGeeks (~99.98%) and Bluehost (99.97%) beat or meet their promise; HostGator measured ~99.89%, below its 99.9% SLA, and A2 Hosting draws reliability complaints. The SLA is a floor the provider sometimes misses.
  3. "100% SLA" means credits, not zero downtime. Liquid Web (VPS/dedicated, 10× credit) and Pressable advertise 100% SLAs — a contractual commitment to compensate for any downtime, not a guarantee it never happens. Check the credit formula and what counts as "downtime."
  4. Five nines is a UCaaS/telephony bar, rarely a shared-hosting one. Nextiva and 8x8 advertise 99.999% (with sub-30s failover for 8x8) because phone outages are business-critical; shared web hosting typically tops out at 99.9–99.99%. Match the nines to how costly an outage actually is for you.
  5. Failover is what turns an SLA into real resilience. Pressable (multi-region auto failover) and 8x8 (sub-30s failover) pair the SLA with architecture that limits a single point of failure — a stronger signal than the percentage alone.

Methodology

The downtime-per-year figures are standard arithmetic on a 365-day year (each additional nine reduces allowed downtime ~10×). Advertised SLAs and measured-uptime figures are compiled from our sourced 2026 hosting and VoIP studies; measured values are third-party monitoring at a point in time and vary by period and configuration. This is a reliability snapshot, not a performance benchmark, and an SLA's value also depends on its credit terms and exclusions.

Editorial note (verification): Measured uptime varies by monitoring window and setup; SLA credit terms and "downtime" definitions differ by provider. Confirm the current SLA, credit formula and recent third-party uptime data before relying on this. Compiled 2026-06-27.

How to cite

"Uptime SLAs Decoded: Advertised vs Measured — 2026", ToolsRanks. https://toolsranks.com/etudes/uptime-sla-vs-measured-2026
Related: Hosting Renewal Shock · Business VoIP Pricing. Dataset on request.