Uptime / SLA Downtime Calculator
Uptime (availability) is the percentage of time a service is up during a period. SLAs often express this as an uptime % target (like 99.9% or 99.99%).
To convert uptime % into allowable downtime, use: downtime = (1 − uptime) × total time. This page calculates it for standard periods and custom day counts.
Note: standard tables often use a 30-day month and 365-day year (this page does).
Calculator
Common SLA Downtime Table
Most teams target 99.9% (≈43m 12s downtime per 30-day month).
| Uptime % | Downtime per Day | Downtime per Week | Downtime per 30-day Month | Downtime per 365-day Year |
|---|---|---|---|---|
| 99% | 14m 24s | 1h 40m 48s | 7h 12m | 3d 15h 36m |
| 99.5% | 7m 12s | 50m 24s | 3h 36m | 1d 19h 48m |
| 99.9% | 1m 26s | 10m 5s | 43m 12s | 8h 45m 36s |
| 99.95% | 43s | 5m 2s | 21m 36s | 4h 22m 48s |
| 99.99% | 9s | 1m 0s | 4m 19s | 52m 34s |
| 99.999% | 1s | 6s | 26s | 5m 15s |
Explanation + FAQs
Why 99.9% isn’t “basically always up”
99.9% sounds extremely high, but it still allows meaningful downtime. For a standard 30-day month, 99.9% uptime permits 43m 12s of downtime. A few short incidents can consume that budget quickly.
SLA vs SLO vs uptime
An SLA is a contract (often with penalties) that defines a minimum uptime/availability. An SLO is an internal target used to manage reliability. Uptime (availability) is the measured outcome.
How monitoring reduces downtime
Better monitoring won’t eliminate incidents, but it reduces time-to-detect and time-to-recover. UpDog provides independent uptime checks, fast SMS alerts / email alerts, and customer-facing status pages.