Uptime & SLA Calculator
99.9% uptime permits 43 minutes 12 seconds of downtime in a 30-day month. Enter your target to see its downtime allowance and remaining error budget.
Calculate your downtime budget
99.9% uptime over 30 days
- Allowed downtime
- 43m 12s
- Remaining budget
- 43m 12s
- Observed availability
- 100%
Calculations run in your browser. No account or paid API is needed. This is time-based availability, not a request-success-rate calculation or a CloudPloy SLA promise.
99.9% vs 99.99%: downtime comparison
| Uptime target | Per day | Per month | Per year |
|---|---|---|---|
| 99% | 14m 24s | 7h 12m | 3d 15h 36m |
| 99.9% | 1m 26.4s | 43m 12s | 8h 45m 36s |
| 99.95% | 43.2s | 21m 36s | 4h 22m 48s |
| 99.99% | 8.64s | 4m 19.2s | 52m 33.6s |
| 99.999% | 0.86s | 25.92s | 5m 15.36s |
For the operational trade-offs, read 99.9% vs 99.99% uptime: choosing a target you can meet.
How to calculate uptime and downtime
Allowed downtime = window length × (100 − target %) ÷ 100
Observed uptime % = (1 − downtime ÷ window length) × 100
Keep the units the same. A 30-day month has 43,200 minutes. At 99.9%, the budget is 43.2 minutes. If your monitor recorded 20 minutes of downtime, 23 minutes 12 seconds remain. This does not predict availability for the rest of the month.
An SLI is the measurement, an SLO is the target, and an SLA is an agreement that may specify service credits. See Google's service level objectives chapter for these definitions.
Uptime calculator questions
How much downtime does 99.9% uptime allow?
99.9% uptime allows 43 minutes 12 seconds of downtime in a 30-day month, or 8 hours 45 minutes 36 seconds in a 365-day year. A 28-day or 31-day month has a different allowance.
What is the difference between 99.9% and 99.99% uptime?
99.99% allows one tenth as much downtime as 99.9%. In a 30-day month, the budget falls from 43 minutes 12 seconds to 4 minutes 19.2 seconds. Both the percentage and the measurement window matter.
How do you calculate an error budget?
For time-based availability, multiply the window length by (100 minus the target percentage) divided by 100. Subtract observed downtime to get the remaining budget. A negative result means the budget has been exceeded.
Does scheduled maintenance count as downtime?
That depends on the SLA or SLO definition. This calculator counts every minute you enter as downtime and makes no automatic exclusions. Check the agreement for maintenance exclusions, partial outages, and eligibility rules.
Is this a website uptime monitor?
No. This calculator works from the numbers you enter. It does not visit your website or measure outages. Use monitoring data for the observed downtime input.