99% uptime SLA
99% uptime allows 7 hours 18 minutes 17 seconds of downtime a month, 14 minutes 24 seconds a day and 3 days 15 hours 39 minutes 29 seconds a year, using a 365.2425-day year. Detecting an outage with 1-minute checks and one confirming retry takes up to 2 minutes, 0.5% of that monthly budget, before anyone starts fixing it.
How much downtime 99% allows, and what it takes to actually meet it.
Allowed downtime
| Period | Allowed downtime | Required uptime |
|---|---|---|
| Daily | 14m 24s | 23h 45m 36s |
| Weekly | 1h 40m 48s | 6d 22h 19m 12s |
| Monthly | 7h 18m 17s | 30d 3h 10m 48s |
| Quarterly | 21h 54m 52s | 90d 9h 32m 25s |
| Yearly | 3d 15h 39m 29s | 361d 14h 9m 42s |
Year = 365.2425 days; month = year ÷ 12 (30.44 days); quarter = year ÷ 4. Rounded down to the second.
What 99% takes in practice
Detection eats into the budget
Monitoring can't alert before it has seen the failure. Worst-case detection is roughly the check interval times the number of failed checks it takes to confirm (confirmation avoids paging on a single network blip).
| Check interval | Failed checks to alert | Worst-case detection | Share of the monthly budget |
|---|---|---|---|
| 5 minutes | 1 | 5m | 1.1% |
| 5 minutes | 2 | 10m | 2.3% |
| 1 minute | 1 | 1m | 0.2% |
| 1 minute | 2 | 2m | 0.5% |
| 30 seconds | 1 | 30s | 0.1% |
| 30 seconds | 2 | 1m | 0.2% |
Dependencies multiply
If your service needs two components that are each 99% available (say, the app and its database), the best you can expect is 99% × 99% ≈ 98.01%, which is 14h 32m 11s of downtime a month. Every hard dependency on the request path lowers the ceiling.
Other SLA levels
| SLA | Per month |
|---|---|
| 99% | 7h 18m 17s |
| 99.5% | 3h 39m 8s |
| 99.9% | 43m 49s |
| 99.95% | 21m 54s |
| 99.99% | 4m 22s |
| 99.999% | 26s |
Know your real uptime, not just the promised one
Vigil checks every minute from several locations and confirms a failure before alerting, so detection stays a small slice of your budget. Monthly SLA reports and a public status page come included.