# Uptime SLA Downtime Calculator

> Convert an uptime percentage such as 99.9% or 99.99% into the downtime it allows per day, week, month, quarter or year, in minutes and seconds.

Category: Software, cloud & AI · Applies to: Worldwide · Last updated: 2026-10-29
Interactive calculator: https://calculators.geekmidst.com/calculators/website-uptime-sla-downtime-calculator

An uptime target leaves a fixed slice of time for outages: the period length × (1 − uptime). At 99.9%, that is 43 minutes 12 seconds in a 30-day month.

Also called: SLA calculator, Availability calculator, Nines calculator.

## Inputs
- Uptime target (unit %; default 99.9)
- Period (options: Day, Week, 30-day month, Average month (30.44 days), Average quarter (91.31 days), 365-day year, Custom number of days; default month30)
- Period length (unit days; default 28)

## Results
- Allowed downtime
- Allowed downtime
- In seconds
- In hours
- Period length

## Formula

```
Allowed downtime = Period length × (1 − Uptime% ÷ 100)
```

Where:
- Period length: the measurement window in minutes (30 days = 43,200 min; 365 days = 525,600 min)
- Uptime%: the availability target

## Worked example
1. A 30-day month is 30 × 24 × 60 = 43,200 minutes.
2. Downtime share: 1 − 0.999 = 0.001.
3. 43,200 × 0.001 = 43.2 minutes = 43 min 12 s.

**Result:** A 99.9% uptime target allows 43 minutes 12 seconds of downtime in a 30-day month (8 h 45 min 36 s a year).

## What the result means

Each extra nine cuts the allowance tenfold: 99.99% leaves about 4.3 minutes a month, which is less than most manual incident responses take. Higher targets need automated failover rather than faster humans.

## Assumptions and limits
- Downtime is measured as whole-service unavailability over the chosen calendar period.
- Real SLAs define what counts as downtime (for example, excluding planned maintenance, or measuring in 5-minute intervals); read your contract’s definition.

## Questions

### Which month length should I use?

Use whatever your SLA uses. Many use a calendar month, so 28 to 31 days; 30 days and the average month (30.44 days) are common approximations.

### Is availability the same as uptime?

Usually yes in SLAs. Request-based SLOs instead count the share of successful requests; use the Error Budget Calculator for those.

## Related calculators
- [Error Budget Calculator](https://calculators.geekmidst.com/calculators/error-budget-calculator)
- [P95 Latency Calculator](https://calculators.geekmidst.com/calculators/p95-latency-calculator)
- [Percentage Calculator](https://calculators.geekmidst.com/calculators/percentage-calculator)
- [Availability Percentage Calculator](https://calculators.geekmidst.com/calculators/availability-percentage-calculator)

Source: GM¹X CalcVerse — https://calculators.geekmidst.com/calculators/website-uptime-sla-downtime-calculator