SLA Uptime Calculator
Calculate annual downtime hours, estimate costs, and compare SLA tiers to find the right reliability level for your business.
SLA Tier Comparison
| SLA Tier | Annual Downtime | Annual Cost | Monthly Downtime |
|---|---|---|---|
| 99.9% | 8h 46m | $43,800 | 0h 44m |
| 99.99% | 0h 53m | $4,380 | 0h 4m |
| 99.999% | 0h 5m | $438 | 0h 0m |
Understanding SLA Tiers
What “99.9% uptime” actually means
SLA percentages look similar on paper but compound very differently over a year. Moving from 99.9% to 99.99% uptime doesn't cut your downtime by a tenth — it cuts it by ninety percent, from roughly 8.7 hours a year to about 52 minutes. That gap is why “three nines vs four nines” is one of the most consequential lines in any MSP contract, and why clients rarely notice the difference until an outage lands during their busiest week.
What counts as downtime
Most SLAs define downtime as any period a covered service is fully unavailable to end users — not degraded performance, not a slow response, full unavailability. Scheduled maintenance windows are typically excluded if proper notice was given (commonly 48–72 hours). Get this definition in writing before committing to a number: an SLA without a clear downtime definition isn't really a commitment.
Common UK MSP tiers
99.9% (“three nines”) is the standard baseline for most business services. 99.95% is common for anything client-facing where reputational risk is higher. 99.99% and above is usually reserved for infrastructure classed as mission-critical — and it costs meaningfully more to deliver reliably, in redundancy, monitoring, and on-call coverage.
The real cost isn't the outage — it's the response
The calculator above prices raw downtime hours, but the bigger driver of client churn is usually how an MSP handles the minutes after something breaks: how fast the alert fires, how fast a technician acknowledges it, and how clearly the client is kept informed while it's being fixed.
Frequently Asked Questions
Is 99.9% uptime good for an MSP client?
It's the standard baseline for most business services, allowing for roughly 8.7 hours of downtime a year. Whether it's “good” depends on how critical the covered service is — client-facing or mission-critical systems usually justify a higher tier.
Does scheduled maintenance count against my SLA?
Usually not, provided proper advance notice was given — commonly 48–72 hours. Confirm this explicitly in the SLA text; it isn't a universal default.
What's the practical difference between 99.9% and 99.99% uptime?
About 90% less downtime — roughly 8.7 hours a year at 99.9% versus about 52 minutes at 99.99%. Delivering that extra reliability typically requires redundant infrastructure and tighter on-call coverage, which is why higher tiers cost more.
How is annual downtime calculated from an uptime percentage?
Multiply (100% − uptime%) by the number of hours in a year (8,760). At 99.9%, that's 0.1% × 8,760 ≈ 8.76 hours. Use the calculator above to run this for any percentage and see the cost impact.
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