Uptime Calculator
Convert an uptime percentage (like 99.9%) into allowed downtime per year, month, and day, the standard SLA 'nines' calculation.
⏰ What is the Uptime Calculator?
This uptime calculator converts an uptime percentage into allowed downtime per year, month, and day, the standard SLA "nines" calculation used to evaluate service-level agreements. Enter an uptime percentage, and it returns your concrete downtime budget.
This calculator reproduces the standard published availability "nines" table exactly, for example, 99.9% uptime gives 8.77 hours of allowed downtime per year, the commonly cited "three nines" benchmark.
Comparing raw uptime percentages can be misleading since the relationship to downtime is nonlinear, converting to an actual time budget makes it much easier to judge whether a commitment meets your real requirements.
This calculator is useful for evaluating cloud provider and SaaS SLA commitments, and for infrastructure and reliability engineering students studying availability targets.
📐 Formula
📖 How to Use This Calculator
Steps
💡 Example Calculations
Example 1 - "Three nines" (99.9%)
Example 2 - "Two nines" (99%)
Example 3 - "Five nines" (99.999%)
❓ Frequently Asked Questions
🔗 Related Calculators
What is uptime?
Uptime is the percentage of time a system, service, or website is operational and available, as opposed to being down due to outages, maintenance, or failures. It is the standard metric used in service-level agreements (SLAs) to specify reliability commitments.
What is the formula for converting uptime percentage to downtime?
Downtime = (1 − uptime%/100) × total time in the period. For a year, total time is 365.25 days (accounting for leap years), converted to minutes for a more readable result at high uptime percentages.
How much downtime does 99.9% uptime allow per year?
99.9% uptime ('three nines') allows about 8.77 hours of downtime per year, a commonly cited SLA benchmark for many commercial cloud services.
What is the 'nines' table for availability?
99% (two nines) ≈ 3.65 days/year, 99.9% (three nines) ≈ 8.77 hours/year, 99.99% (four nines) ≈ 52.6 minutes/year, 99.999% (five nines) ≈ 5.26 minutes/year. Each additional nine reduces allowed downtime by roughly a factor of 10.
Why is achieving 'five nines' (99.999%) so much harder than 'three nines' (99.9%)?
Five nines allows only about 5 minutes of downtime per year, compared to nearly 9 hours for three nines, a roughly 100x tighter budget. Achieving this requires redundant infrastructure, automated failover, and extremely fast incident response, dramatically increasing engineering and operational cost.
Does this calculator account for planned maintenance downtime?
No, this calculator computes the total allowed downtime budget for a given uptime percentage, regardless of cause. Many real SLAs separately exclude scheduled maintenance windows from the uptime calculation, check your specific provider's SLA terms for those exclusions.
What is a typical SLA uptime commitment from major cloud providers?
Many major cloud services commonly publish SLA commitments in the 99.9% to 99.99% range for standard tiers, with higher-availability configurations sometimes offering 99.99% or better for an additional cost.
How is downtime per month calculated from the yearly figure?
This calculator divides the yearly downtime evenly by 12 to estimate a monthly figure, a simplification since real downtime is rarely distributed perfectly evenly across months, but useful as a planning benchmark.
Can uptime percentage be 100%?
In practice, no system achieves a mathematically perfect 100% uptime over any meaningful timeframe, this calculator requires an uptime value strictly less than 100% since dividing by zero downtime has no meaningful result to display.
Why does this matter for choosing a service provider?
Comparing SLA uptime percentages directly can be misleading since the relationship is nonlinear. Converting each provider's stated uptime commitment into an actual downtime budget makes it much easier to judge whether a service meets your real availability requirements.