Uptime SLA & Downtime Calculator
Convert service availability percentages (99%, 99.9%, 99.99%) into exact allowed downtime budgets per day, week, month, and year.
⚡ Quick Reference Rule:
Three Nines (
99.9% availability) allows 43 minutes and 49 seconds of downtime per month. Four Nines (99.99% availability) cuts your monthly downtime budget to just 4 minutes and 23 seconds. Five Nines (99.999%) allows only 26.3 seconds per month.
Choose whether your SLA agreement applies round-the-clock or during working hours only.
Three Nines (99.9%)
Standard Production
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Daily Allowed Downtime
1m 26s
Weekly Allowed Downtime
10m 4s
Monthly Allowed Downtime (30.4 days)
43m 49s
Quarterly Allowed Downtime (91.3 days)
2h 11m 29s
Annual Allowed Downtime (365.25 days)
8h 45m 57s
Monthly SRE Error Budget
43m 49s / month
Reverse Lookup: Calculate SLA Uptime % from Outage Duration
minutes of outage in a
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High Availability & The "Nines" Reference Table
In cloud computing and Site Reliability Engineering (SRE), service reliability is commonly communicated through percentages of uptime known as "the nines". Here is the canonical breakdown for continuous 24/7/365 operations:
| Availability Level | Daily Downtime | Weekly Downtime | Monthly Downtime | Yearly Downtime |
|---|---|---|---|---|
| 90% (One Nine) | 2 hours, 24 minutes | 16.8 hours | 3.04 days | 36.5 days |
| 99% (Two Nines) | 14 minutes, 24 seconds | 1 hour, 40 minutes | 7 hours, 18 minutes | 3.65 days |
| 99.5% | 7 minutes, 12 seconds | 50 minutes, 24 seconds | 3 hours, 39 minutes | 1.83 days |
| 99.9% (Three Nines - SaaS Standard) | 1 minute, 26 seconds | 10 minutes, 4 seconds | 43 minutes, 49 seconds | 8 hours, 45 minutes |
| 99.95% (High Availability SaaS) | 43.2 seconds | 5 minutes, 2 seconds | 21 minutes, 54 seconds | 4 hours, 22 minutes |
| 99.99% (Four Nines - Enterprise Cloud) | 8.6 seconds | 1 minute, 0.5 seconds | 4 minutes, 23 seconds | 52 minutes, 35 seconds |
| 99.999% (Five Nines - Carrier Grade) | 0.86 seconds | 6.05 seconds | 26.3 seconds | 5 minutes, 15 seconds |
| 99.9999% (Six Nines - Life Critical) | 0.086 seconds | 0.60 seconds | 2.63 seconds | 31.5 seconds |
Understanding SLA, SLO, and SLI in SRE
Modern DevOps and Site Reliability Engineering frameworks distinguish between three interconnected availability metrics:
- SLI (Service Level Indicator): A quantifiable measurement of service performance in real time (e.g., HTTP 200 response rate or 99th-percentile response latency).
- SLO (Service Level Objective): The internal target reliability set by the engineering team (e.g., 99.95% successful requests over a 30-day rolling window).
- SLA (Service Level Agreement): The formal legal contract with customers committing to a specific availability floor (e.g., 99.9%), usually backed by financial remedies such as service credits or penalty refunds.
- Error Budget:
100% - SLO. The total permitted unreliability or downtime a product can experience in a billing cycle before engineering halts feature releases to focus exclusively on reliability.
Architectural Strategies to Achieve 99.99% Availability
Moving from Three Nines (99.9%) to Four Nines (99.99%) requires eliminating all single points of failure (SPOF) and automating failover:
- Multi-Availability Zone (Multi-AZ) Redundancy: Deploy database clusters and compute nodes across at least 3 isolated physical data centers within a cloud region.
- Automated Health Probes & Self-Healing: Kubernetes liveness probes and cloud load balancers must automatically isolate unhealthy pods or instances within seconds.
- Zero-Downtime Rolling & Blue/Green Deployments: Application updates must deploy gradually without severing active client TCP connections.
- Multi-Region Disaster Recovery: Cross-region active-passive or active-active replication to withstand full cloud region disruptions.
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