How is uptime percentage calculated?

Uptime percentage is calculated using the formula: Availability (%) = (Total Time - Downtime) / Total Time × 100. For example, if a service ran for 720 hours in a month with 43 minutes of downtime, the availability would be 99.9%.

How much downtime does a 99.9% SLA allow?

A 99.9% SLA (three nines) allows approximately: 43.8 minutes per month, 10.1 minutes per week, 1.44 minutes per day, or 8.76 hours per year. This is the standard for most production services.

What is the difference between 99.9% and 99.99% availability?

99.9% (three nines) allows ~43.8 minutes of downtime per month, suitable for standard production applications. 99.99% (four nines) allows only ~4.38 minutes per month, requiring redundant infrastructure and high availability. The difference can cost significantly more in infrastructure.

What is an SLA and how does it relate to downtime?

An SLA (Service Level Agreement) is a contract that defines the expected service level, including the guaranteed uptime percentage. For example, a 99.9% SLA means the provider guarantees the service will be available 99.9% of the time, and any downtime below that threshold may result in credits or penalties.

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99.999% SLA - Downtime Calculator

Select an SLA level or enter downtime minutes to see the allowed downtime per period.

SLA 99% SLA 99.9% SLA 99.95% SLA 99.99% SLA 99.999% SLA 99.9999%

Availability & SLA Calculator

Calculate availability from downtime or downtime from SLA requirement

Downtime minutes per month

Enter the downtime minutes for each month to get a more accurate annual average.

Select SLA level

Maximum allowed downtime

SLA Level	Day	Week	Month	Quarter	Year	Typical use
99%	14 min 24 s	1 h 41 min	7 h 12 min	21 h 36 min	3 d 16 h	Dev / testing
99.9%	1 min 26 s	10 min 5 s	43 min 12 s	2 h 10 min	8 h 46 min	Standard production
99.95%	43 s	5 min 2 s	21 min 36 s	1 h 5 min	4 h 23 min	High availability
99.99%	9 s	1 min	4 min 19 s	12 min 58 s	52 min 34 s	Enterprise
99.999%	< 1 s	6 s	26 s	1 min 18 s	5 min 15 s	Mission critical
99.9999%	< 1 s	< 1 s	3 s	8 s	32 s	Fault tolerant

Downtime cost calculator

Hourly revenue ($)

What is availability?

Availability measures the percentage of time a service is operational. It is calculated by subtracting downtime from total time divided by total time. It is the most common metric used in SLA contracts to guarantee service quality.

Availability (%) = (Total Time - Downtime) / Total Time × 100

Example: 30 days = 720h. If the service was down 7.2h: (720 - 7.2) / 720 × 100 = 99% availability

What is an SLA?

An SLA (Service Level Agreement) is a contract between provider and customer that defines the minimum acceptable service level. It typically includes guaranteed uptime percentage, maximum incident response time (MTTR), and penalties for non-compliance.

Why percentiles matter

The gap between 99.9% and 99.99% is massive: the former allows 43 minutes of downtime per month, the latter only 4.3 minutes. For an e-commerce site earning $100k/day, 1 hour of downtime costs ~$4,166. Choosing the right SLA is a business decision, not a technical one.

Mean time metrics

MTBF (Mean Time Between Failures) = Total Operational Time / Number of Failures
MTTR (Mean Time To Repair) = Total Repair Time / Number of Repairs
MTTA (Mean Time To Acknowledge) = Total Time to Acknowledge / Number of Incidents

SLA Service Credit

Typical penalty when SLA is not met:

• Below 99.9% but ≥ 99.0% → 10% credit
• Below 99.0% → 25% credit

What Does a 99.999% SLA Mean?

A 99.999% SLA, known as five nines, is the highest standard availability level in the commercial industry. It guarantees a system is operational 99.999% of the time, allowing only 26 seconds of downtime per month or 5.26 minutes per year. If the service went down just one minute beyond the agreed threshold, the provider would breach the contract. This level is non-negotiable in environments where seconds of interruption can result in millions in losses, security risks, or disruption to thousands of users.

Who Is It For?

Five nines SLA is designed for industries where service discontinuity has catastrophic consequences. Algorithmic trading and fintech: exchanges and payment systems lose millions per minute. Telecommunications: carrier operators supporting critical communications. Emergency services: 911 systems, defense communications, air traffic control, and power grids. Enterprise SaaS platforms with multi-million dollar contracts that include severe penalty clauses also adopt this level.

Infrastructure Requirements

Sustaining 99.999% availability requires 20-50x the investment of a 99.9% SLA. You need data centers in at least three geographically separated regions with automatic failover in milliseconds. Redundancy must be N+2 or higher: every component has at least two complete backups. Failover must be instantaneous using DNS anycast, BGP multi-homing, and global load balancing. Dedicated 24/7 SRE teams with automated runbooks and weekly chaos engineering tests are mandatory.

Cost

A 99.999% SLA costs 20-50x more than 99.9%. For most businesses this investment is not justified, but for sectors where each minute of downtime represents millions in losses, it is the only viable option. A trading exchange processing $10M per day cannot afford even a minute of downtime — the multi-region N+2 infrastructure investment pays for itself by preventing a single 5-minute outage per year.

When to Upgrade?

You should consider migrating to five nines when the cost of each minute of downtime exceeds the additional infrastructure investment, when client contracts explicitly require this level, when operating in regulated sectors (finance, healthcare, telecommunications), or when your current architecture can no longer scale redundancy. If you are not ready yet, check our 99.99% enterprise SLA as an intermediate step. For absolute fault tolerance, explore 99.9999% fault tolerant SLA.

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