How do you calculate availability?

Availability (%) = (Total Time − Downtime) / Total Time × 100. For example, a service that was down 7.3 hours in a 30-day month (720 hours) has an availability of (720 − 7.3) / 720 × 100 = 98.99%.

How much downtime does 99.9999% uptime allow?

At 99.9999% uptime, the maximum allowed downtime is 86ms per day, 3 seconds per 30-day month, and 32 seconds per 365-day year.

What's the difference between 99.9% and 99.99% uptime?

Each additional nine reduces allowed downtime tenfold: 99.9% allows about 8 hours 46 minutes of downtime per year, while 99.99% allows just under 53 minutes. Meeting 99.99% generally requires automated failover, since a human response rarely fits inside the budget.

How do I track SLA compliance?

Continuous uptime monitoring measures availability from outside your infrastructure and records every outage. Hyperping checks your endpoints at up to 30-second intervals from multiple regions and reports uptime, MTTR, and SLA compliance over any period.

Is six nines uptime realistic?

Six nines can be realistic for a narrowly defined, highly redundant service, but it is exceptionally demanding for an entire user journey. The yearly downtime budget is about 32 seconds, so measurement scope and dependency failures matter greatly.

Six Nines (99.9999%) Uptime: How Much Downtime Is That?

Six nines: a hardware spec, not a service promise

99.9999% availability is 32 seconds of downtime per year, or 3 seconds a month. No meaningful incident response fits inside that window, so the system cannot recover from failures. It has to mask them entirely.

You will encounter the figure in network equipment datasheets and storage array marketing, where it describes how rarely a component fails under controlled conditions. Stack those components into a real distributed system and combined availability falls below the weakest link, which is why service SLAs sit several nines lower.

Nobody holds 99.9999%.

Measure the uptime you actually deliver.

A number nobody can verify is marketing. A measurement is not.

Hyperping checks every 30 seconds from 18 locations and alerts you before the budget is gone: Slack, SMS, phone call, PagerDuty.

Free plan · no credit card · first check in under a minute

Enter an endpoint. The first check runs in under a minute.

Promising 99.9999% to customers? Show it on a status page they can see, from $29/mo with monitoring included →

Why 6 9s does not survive contact with a real system

At that threshold conventional operations stop applying: maintenance windows cannot exist, restarts must be invisible, and detection itself has to complete in under a second to leave any time for mitigation. Measurement turns philosophical too, since a 30-second check interval cannot reliably observe an outage shorter than the entire annual budget.

Reaching it end to end would mean eliminating every single point of failure, including the third parties you do not control: DNS, certificates, upstream providers, each carrying its own budget. If a contract offers six nines, the exclusions section is doing all the work. Read it before pricing the promise.

How serial dependencies erase six nines

Ten required components rated at 99.9999% combine to about 99.999% even when their failures are independent. A service can lose an entire nine simply by placing reliable components in series.

Real systems also share power, networks, software releases, and operators, so independence is an optimistic assumption. Six-nines hardware can support a resilient design, but it cannot guarantee the availability users observe.

Engineering for failure masking, not recovery

A system at this level cannot wait for a failed node to restart. It needs active capacity in separate failure domains, quorum rules that tolerate a loss instantly, and routing that removes unhealthy paths without interrupting requests.

Maintenance has to use the same masking mechanisms as an incident. Reboots, certificate rotation, schema changes, and network work must happen one isolated slice at a time while the remaining capacity carries the full load.

What to demand from a six-nines contract

The contract should identify the exact transaction, measurement frequency, geographic scope, latency threshold, and treatment of planned work. It should also explain how an outage shorter than the probe interval can be discovered and counted.

Require historical evidence for the whole service rather than a hardware MTBF figure or one narrow subsystem. If the provider cannot produce measurement data at finer resolution than the annual allowance, the promise is not auditable.

Downtime allowed at each SLA level

Uptime	Per day	Per month	Per year
99% Two nines	14m 24s	7h 12m	3d 15h
99.9% Three nines	1m 26s	43m 12s	8h 45m 36s
99.95%	43s	21m 36s	4h 22m 48s
99.99% Four nines	9s	4m 19s	52m 34s
99.999% Five nines	864ms	26s	5m 15s
99.9999% Six nines	86ms	3s	32s
99.9999999% Nine nines	86μs	2.6ms	32ms

SLA calculation cheatsheet

Availability calculation

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

Example: If a service was down for 7.3 hours in a 30-day month:

Total Time = 30 days × 24 hours = 720 hours
Availability = (720 - 7.3) / 720 × 100 = 98.99%

Response time SLA

Response Time Compliance (%) = (Responses Within Threshold / Total Responses) × 100

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

Service credit calculation

Service Credit = (Monthly Service Fee) × (Credit Percentage for SLA Breach)

SLA penalty example

If availability drops below 99.9% but remains above 99.0%: 10% credit
If availability drops below 99.0%: 25% credit

Track SLAs and downtime metrics at a glance

Hyperping reports on service reliability using data collected by your monitors. Select the reporting period, then review the results in the dashboard or export them.

Track uptime, Mean Time to Recovery (MTTR), and SLA compliance for any reporting period.
Export the selected period as a CSV file for audits, client reports, spreadsheets, or internal analysis.
Review the complete incident history and use filters to narrow the records included in your report.

Monitor reporting dashboard showing outages, MTTR, and SLA metrics over time →

Monitor reporting analytics — Monitor reporting dashboard showing outages, MTTR, and SLA metrics over time →

SLA & uptime management guides

Incident Management: Best Practices, Tools Guide & MoreIn this guide, we'll walk through everything you need to know about incident management, from basic concepts to advanced strategies used by top DevOps teams.Understanding SLAs, SLOs, and SLIsSLAs, SLOs, and SLIs are crucial for managing tech services, ensuring reliability and trust. Learn how these elements work together to maintain service quality and user satisfaction.MTTR guide: how to improve system reliability & response timeMeantime to repair (MTTR) directly impacts your customer trust and company reputation. This guide provides actionable steps to boost your system reliability and keep customers happy.

What is uptime?

Uptime is the amount of time that a service is available and operational, typically expressed as a percentage over a given period such as a month or a year.

What is an SLA?

A service-level agreement (SLA) defines the level of service you expect from a vendor, laying out the metrics by which service is measured, as well as remedies or penalties should agreed-on service levels not be achieved.

How to prevent downtime?

Redundancy, monitoring and alerting are key to ensure a safe and reliable service.

Frequently asked questions

How do you calculate availability?: Availability (%) = (Total Time − Downtime) / Total Time × 100. For example, a service that was down 7.3 hours in a 30-day month (720 hours) has an availability of (720 − 7.3) / 720 × 100 = 98.99%.
How much downtime does 99.9999% uptime allow?: At 99.9999% uptime, the maximum allowed downtime is 86ms per day, 3 seconds per 30-day month, and 32 seconds per 365-day year.
What's the difference between 99.9% and 99.99% uptime?: Each additional nine reduces allowed downtime tenfold: 99.9% allows about 8 hours 46 minutes of downtime per year, while 99.99% allows just under 53 minutes. Meeting 99.99% generally requires automated failover, since a human response rarely fits inside the budget.
How do I track SLA compliance?: Continuous uptime monitoring measures availability from outside your infrastructure and records every outage. Hyperping checks your endpoints at up to 30-second intervals from multiple regions and reports uptime, MTTR, and SLA compliance over any period.
Is six nines uptime realistic?: Six nines can be realistic for a narrowly defined, highly redundant service, but it is exceptionally demanding for an entire user journey. The yearly downtime budget is about 32 seconds, so measurement scope and dependency failures matter greatly.