SLA Uptime Calculator
Enter an uptime percentage to see the maximum allowed downtime for each time period.
The "Nines" of Availability
Service availability is commonly expressed as a number of "nines" — the count of 9s in the uptime percentage. Each additional nine reduces the allowed downtime by roughly 10×, making each tier progressively harder (and more expensive) to achieve.
SLA Tiers — Downtime Budget
| Nines | Uptime % | Per Year | Per Month |
|---|---|---|---|
| One nine | 90% | 36.5 days | 73 hours |
| Two nines | 99% | 3.65 days | 7.31 hours |
| Three nines | 99.9% | 8.77 hours | 43.8 min |
| Four nines | 99.99% | 52.6 minutes | 4.38 min |
| Five nines | 99.999% | 5.26 minutes | 26.3 sec |
| Six nines | 99.9999% | 31.6 seconds | 2.63 sec |
SLA vs SLO vs SLI
SLI
Service Level Indicator
A measured metric: request success rate, latency p99, error rate. Raw numbers from your monitoring system.
SLO
Service Level Objective
Your internal target for an SLI: "99.9% of requests return 2xx within 200ms." Internal — no contractual obligation.
SLA
Service Level Agreement
A contract with a customer. Breaching it has financial or legal consequences. Usually looser than your internal SLO.
Frequently Asked Questions
Does planned maintenance count against uptime?▼
It depends on your SLA contract. Many SLAs exclude scheduled maintenance windows from uptime calculations, provided adequate notice is given (typically 48–72 hours). Always check the specific SLA language.
What uptime do most cloud providers guarantee?▼
Most major cloud providers (AWS, GCP, Azure) offer 99.9% to 99.99% SLAs for managed services. Compute instances (VMs) are typically 99.9% to 99.95%. Databases and serverless often get 99.99%. Mission-critical multi-region setups can achieve 99.999%.
What is an error budget?▼
An error budget is the maximum allowable downtime or errors within a period, derived from the SLO. If your SLO is 99.9%, you have a 0.1% error budget (about 43.8 minutes per month). When the budget is exhausted, feature work pauses and reliability work takes priority.
How do I calculate downtime from an SLA percentage?▼
Downtime = total_period_seconds × (1 - uptime_percentage / 100). For 99.9% over a year: 31,556,952 × 0.001 = 31,557 seconds = 8.77 hours. This calculator does it instantly for any percentage and period.