Convert SLA uptime percentages into allowed downtime per year, month, week, and day. Plan service level agreements for ISPs, hosting providers, and enterprise infrastructure with realistic availability targets.
Overview
The SLA Uptime Calculator converts a service level agreement uptime percentage into the maximum allowed downtime per day, week, month, and year. It helps ISPs, hosting providers, managed service providers, and enterprise teams set realistic availability targets and understand what a promised percentage actually means in real time.
Common Use Cases
Service level agreement planning
Uptime commitment negotiation
Hosting and cloud availability review
ISP service target setting
Managed service contract design
Infrastructure availability auditing
Customer expectation management
Maintenance window planning
SLA compliance reporting
Comparing availability tiers
How to Use
1
Enter the uptime percentage promised in the service level agreement, such as 99.9 or 99.99.
2
Use the quick tier buttons to select a common availability target.
3
Review the allowed downtime per day, week, month, and year.
4
Compare the selected target against common SLA tiers in the reference table.
Example Scenario
99.9% Uptime ISP
An ISP promises 99.9% availability on a residential fiber plan. This allows roughly 8.76 hours of downtime per year, or about 43.8 minutes per month, before the provider breaks its SLA commitment.
Technical Notes
Downtime is calculated as the time unavailable during the measurement period. For 99.9% uptime, downtime is 0.1% of the year, or about 8.76 hours.
The number of nines indicates the availability class. 99% is two nines, 99.9% is three nines, 99.99% is four nines, and 99.999% is five nines.
Calculations use 365 days per year. Monthly downtime is one twelfth of the yearly downtime.
SLA uptime may or may not exclude scheduled maintenance windows depending on the specific contract terms.
Reaching four or five nines usually requires redundant power, network, and hardware with automatic failover rather than a single component design.
Common Mistakes
Treating 99.9% and 99.99% as nearly the same
Promising five nines without redundant infrastructure
Forgetting scheduled maintenance exclusions in the SLA
Ignoring third-party dependencies outside the provider control
Measuring uptime from the customer side without agreed rules
Offering credit terms that are too weak to encourage improvement
Frequently Asked Questions
99.9% uptime allows about 8.76 hours of downtime per year, about 43.8 minutes per month, and about 1.44 minutes per day.
99.99% allows about 52.6 minutes of downtime per year, roughly ten times less than the 8.76 hours allowed by 99.9%.
Many SLAs exclude scheduled maintenance windows, but the exact terms must be defined in the contract to avoid disputes.
The number of nines is a shorthand for the availability class. Each additional nine reduces the allowed downtime by roughly a factor of ten.
Higher availability requires more expensive redundancy and engineering. Choose a target that matches the business criticality of the service.
Related Topics
Service level agreementUptime monitoringAvailability tiersNetwork reliabilityFault toleranceRedundant infrastructureMaintenance windowsISP service qualityHosting reliabilitySLA credits