System Availability SLA Calculator
99.9% uptime = 8.76 hours downtime/year. 99.99% = 52 minutes. 99.999% = 5 minutes 15 seconds — less time than your last database failover took. The nines are an engineering budget with a dollar value. Too many nines and your infrastructure cost exceeds the revenue loss you're preventing. Quantify the trade-off.
🎯 SLA Configuration
Select SLA target (90% to 99.9999%). The engine computes allowed downtime per day/month/year. Compare against common incident durations — a typical DB failover alone eats 2-5 minutes.
📋 SLA Downtime Reference Table
The Mathematics of Availability: Why Every 9 Costs Exponentially More
System availability is measured in "nines" — the percentage of time a service is operational. The difference between 99% and 99.999% may seem small on a dashboard, but in downtime terms it's the difference between 3.65 days per year and 5.26 minutes per year. Each additional nine roughly doubles the engineering investment required — redundancy, failover automation, chaos engineering, and on-call staffing all scale with the number of nines you promise.
The Error Budget Concept (Google SRE)
Google's Site Reliability Engineering framework introduces the error budget: the inverse of your uptime SLA. If your SLO is 99.9%, your error budget is 0.1% of the time — about 43.8 minutes per month. This budget is deliberately consumed by planned maintenance, feature rollouts, and acceptable failures. When the budget is exhausted, all feature launches freeze until reliability is restored. The error budget transforms the adversarial relationship between dev and ops into a data-driven negotiation.
Realistic SLA Targets by Service Tier
99% (Two Nines) — 3.65 days/year downtime. Appropriate for internal tools and batch processing. 99.9% (Three Nines) — 8.76 hours/year. Typical for SaaS APIs and business applications. 99.99% (Four Nines) — 52.6 minutes/year. Required for payment processing and critical infrastructure. 99.999% (Five Nines) — 5.26 minutes/year. Carrier-grade telecom and life-critical systems. Each tier requires approximately an order of magnitude more in infrastructure spend than the previous one.