Network Uptime & Five Nines SLA Calculator
Turn an availability percentage into real downtime budgets, estimate the revenue at risk, and see how cascading dependencies quietly destroy your composite SLA.
SLA & Downtime Budget Converter
Move the slider, pick a preset, or type an exact availability value.
Real-World Impact & Revenue Loss Estimator
See the annual revenue and transactions at risk at each SLA tier — and what buying better infrastructure saves you.
Composite SLA & System Cascade Calculator
Model a serial dependency chain. Overall availability = the product of every component's availability.
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SLA Downtime Reference Table
Maximum allowed downtime from 99% through 99.9999%, based on a 365-day year and the average 30.4375-day month.
| SLA | Per Day | Per Week | Per Month | Per Year |
|---|---|---|---|---|
| 99% (Two Nines) | 14m 24s | 1h 40m 48s | 7h 18m 18s | 3d 15h 36m |
| 99.5% (Two-and-a-half Nines) | 7m 12s | 50m 24s | 3h 39m 9s | 1d 19h 48m |
| 99.9% (Three Nines) | 1m 26.4s | 10m 4.8s | 43m 49.8s | 8h 45m 36s |
| 99.95% (Three-and-a-half Nines) | 43.2s | 5m 2.4s | 21m 54.9s | 4h 22m 48s |
| 99.99% (Four Nines) | 8.64s | 1m 0.48s | 4m 23.0s | 52m 33.6s |
| 99.999% (Five Nines) | 864 ms | 6.05s | 26.3s | 5m 15.4s |
| 99.9999% (Six Nines) | 86 ms | 605 ms | 2.63s | 31.5s |
Why "Nines" Matter
The Order-of-Magnitude Trap
Going from 99% to 99.9% looks like a 0.9% improvement, but it cuts annual downtime tenfold — from 87.6 hours to 8.76 hours. Every additional nine divides the allowed outage by ten again: 99.99% allows 52 minutes, and 99.999% allows just over 5 minutes a year. Because the value is so concentrated near 100%, the difference between tiers is far larger than the percentages suggest.
Why Composite SLAs Are Worse Than They Look
When components are arranged in series, availability multiplies. Four components at 99.9% produce 99.60% overall — roughly 35 hours of downtime per year even though every single tier met its target. In a serial chain every component is a single point of failure, so the weakest link sets the ceiling. To raise the composite, improve the weakest component first: it delivers the largest marginal gain.
ROI of One Extra Nine
For a service earning $5,000 per hour, moving from 99.9% to 99.99% removes about 8.2 hours of annual outage — roughly $41,000 in avoided loss per year — and reaching 99.999% saves about $43,000 versus the three-nines baseline. That is the budget that redundant infrastructure, failover and multi-AZ architectures are expected to justify.
How Downtime Is Measured
Downtime is computed as (1 − SLA) × period length. A 365-day year has 8,760 hours; the average month uses 30.4375 days (730.5 hours); a week is 168 hours; a day is 24 hours (86,400 seconds). Most vendors quote SLA budgets against the 365-day year, but if you are auditing a specific leap year, use the 366-day toggle in this calculator.
Frequently Asked Questions
What is the difference between uptime and SLA?
Uptime is the measured percentage of time a service was actually operational over a given window. An SLA (Service Level Agreement) is the contractual commitment a provider makes — the minimum availability you are entitled to. If a provider commits to a 99.9% SLA, they are promising no more than about 8.76 hours of downtime per year; if real uptime falls below the SLA target, the provider typically owes service credits or penalties.
What does "five nines" availability mean?
Five nines means 99.999% availability, which allows only about 5.26 minutes of downtime per year — roughly a single deep breath. Each additional nine cuts the allowed downtime by an order of magnitude: 99.9% allows 8.76 hours, 99.99% allows 52.56 minutes, and 99.999% allows 5.26 minutes per year. Five nines is the target for carrier-grade telecom and critical infrastructure.
How much downtime is allowed with a 99.9% SLA?
With a 99.9% SLA the allowed downtime is 0.1% of the period: about 8 hours 45 minutes per year, 43 minutes per month, 10 minutes per week, and 1 minute 26 seconds per day. Use this calculator to see the exact budgets for any SLA value from 90% up to 99.9999%.
How do I calculate the composite SLA of multiple services?
When services depend on each other in a serial chain, multiply their availability fractions. For example, four components each at 99.9% give 0.999 × 0.999 × 0.999 × 0.999 = 0.996006, or 99.60% overall — about 35 hours of downtime per year even though every single component met its target. This is why composite reliability drops fast and why every component is effectively a single point of failure.
How do I convert a recorded outage into an achieved SLA percentage?
Subtract the outage duration from the total time in the window, divide by the total time, and multiply by 100. For example, if a service was down for 2 hours in a 30-day month, achieved SLA = (720 − 2) / 720 × 100 = 99.72%. Compare that figure against your contractual target — if it falls below the target, the SLA was breached.
Does a leap year change downtime calculations?
Yes. A 366-day leap year contains 8,784 hours versus 8,760 in a common year, so the same SLA percentage allows slightly more absolute downtime. For a 99.9% SLA that difference is about 2.4 minutes. Most vendors quote SLAs against a 365-day year, but if you are measuring a specific leap year, toggle the leap-year option in this calculator for exact figures.