Calculate allowed downtime at every SLA level, estimate the financial impact of outages, and understand what each “nine” of availability really means for your business.
| SLA Level | Downtime / Month | Downtime / Year | Tier Name | Typical Use |
|---|---|---|---|---|
| 99% | 7h 18m | 3d 15h 36m | Two Nines | Budget hosting, dev/test |
| 99.5% | 3h 39m | 1d 19h 48m | — | Standard broadband |
| 99.9% | 43m 50s | 8h 45m 36s | Three Nines | Business-grade services |
| 99.95% | 21m 55s | 4h 22m 48s | — | Enterprise cloud |
| 99.99% | 4m 23s | 52m 34s | Four Nines | High-availability |
| 99.999% | 26s | 5m 15s | Five Nines | Carrier-grade |
Downtime is calculated as (1 - SLA%) × total hours in the period. Monthly = 730 hours, yearly = 8,760 hours. Actual SLA terms vary by provider. Talk to our network team
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A 99.9% uptime SLA allows roughly 43 minutes of downtime per month, or about 8.7 hours per year. It sounds close to 100%, but for a business relying on cloud applications or VoIP throughout the working day, that downtime can still translate into meaningful disruption if it lands during peak hours.
Moving from 99.9% to 99.99% cuts allowed downtime from about 43 minutes a month to roughly 4.3 minutes — a tenfold improvement. Achieving that extra reliability usually requires redundant infrastructure, failover connections, and more expensive service tiers, so it is worth weighing the cost against how downtime-sensitive your operations really are.
Most UK SMEs are well served by 99.9% for general connectivity and cloud services, reserving 99.95% or 99.99% for mission-critical systems like e-commerce platforms or VoIP where every minute of outage has a direct revenue or customer-service impact. Higher SLAs typically come at a premium cost.
Uptime percentage is calculated as total available time minus downtime, divided by total available time, expressed as a percentage over a given period. This calculator converts common SLA percentages like 99.9%, 99.95%, and 99.99% directly into real minutes and hours of allowed downtime per month and per year for easy comparison.
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