Uptime SLA Calculator
Calculate allowed downtime based on SLA uptime percentage. Supports common SLA tiers like 99.9% (Three Nines) and 99.99% (Four Nines).
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What is uptime and why does it matter?
Uptime refers to the amount of time a system, service, or application remains operational and accessible to users. It's typically expressed as a percentage of total time over a given period. For example, 99.9% uptime means a service is expected to be available 99.9% of the time.
Uptime is a critical metric for any online service because it directly impacts user experience, business revenue, and brand reputation. When a website or application goes down, users can't access it, transactions fail, and trust erodes. For e-commerce sites, even minutes of downtime during peak hours can translate to thousands of dollars in lost sales.
What is an SLA?
A Service Level Agreement (SLA) is a formal contract between a service provider and its customers that defines the expected level of service. The uptime percentage is one of the most important metrics in any SLA. Cloud providers, hosting companies, and SaaS vendors typically guarantee a specific uptime percentage, and if they fail to meet it, customers may be entitled to service credits or refunds.
Understanding the "Nines" of availability
The industry uses a shorthand called "nines" to describe availability levels:
| Availability | Name | Annual Downtime | Monthly Downtime |
|---|---|---|---|
| 99% | Two Nines | 3 days 15 hr | 7 hr 12 min |
| 99.9% | Three Nines | 8 hr 45 min | 43 min 11 sec |
| 99.95% | Three and a Half Nines | 4 hr 22 min | 21 min 35 sec |
| 99.99% | Four Nines | 52 min 33 sec | 4 min 19 sec |
| 99.999% | Five Nines | 5 min 15 sec | 25.92 sec |
| 99.9999% | Six Nines | 31.54 sec | 2.59 sec |
Each additional "nine" represents a 10x improvement in availability but typically requires exponentially more investment in infrastructure, redundancy, and operational practices.
How is downtime calculated?
Downtime is calculated as the inverse of uptime. If a service has 99.9% uptime, the allowed downtime is 0.1% of the total time period. The formula is:
Allowed Downtime = Total Period × (100% - Uptime%)
For example, with 99.9% uptime over a year:
- Total period: 365 days = 525,600 minutes
- Downtime percentage: 0.1% = 0.001
- Allowed downtime: 525,600 × 0.001 = 525.6 minutes ≈ 8.77 hours
Tool description
This Uptime SLA Calculator helps you convert between uptime percentages and allowed downtime across different time periods. It supports two calculation modes:
Uptime to Downtime: Enter an uptime percentage (like 99.9%) and instantly see the maximum allowed downtime per day, week, month, and year.
Downtime to Uptime: Enter your acceptable downtime in minutes for a specific period, and the calculator will show you what uptime percentage that represents.
This bidirectional approach makes it easy to plan SLAs from either direction—whether you're setting targets based on industry standards or working backward from operational constraints.
Examples
Example 1: Three Nines (99.9%) Uptime
- Input: 99.9% uptime
- Output:
- Daily: 1 minute 26 seconds
- Weekly: 10 minutes 4 seconds
- Monthly: 43 minutes 11 seconds
- Yearly: 8 hours 45 minutes
Features
- Bidirectional calculation: Convert uptime percentage to downtime or downtime to uptime percentage
- Multiple time periods: View downtime allowances for daily, weekly, monthly, and yearly periods simultaneously
- Precise calculations: Handles high-precision percentages up to six nines (99.9999%) and beyond
- Human-readable output: Displays results in the most appropriate units (seconds, minutes, hours, or days)
- Real-time updates: Results update instantly as you type
Use cases
SLA negotiations: When negotiating contracts with cloud providers or hosting companies, quickly understand what different uptime guarantees actually mean in terms of acceptable downtime.
Infrastructure planning: Determine the redundancy and failover capabilities needed to achieve a target uptime percentage based on your maintenance windows and expected incident response times.
Incident post-mortems: After an outage, calculate how the downtime affects your SLA compliance for the month or year and determine remaining downtime budget.
Comparing service providers: Evaluate different vendors by translating their uptime guarantees into concrete downtime numbers that are easier to compare and understand.
Setting realistic targets: Work backward from your team's operational capabilities (maintenance schedules, deployment windows, incident response time) to determine what uptime percentage you can realistically promise to customers.