---
title: "Uptime Calculator - SLA Percentage"
description: "Calculate uptime percentage, allowed downtime, and SLA metrics from uptime ratio or downtime duration over any period."
image: "https://onlineminitools.com/tools/uptime-calculator/logo.svg"
---

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# Uptime Calculator

Calculate uptime percentage, allowed downtime, and SLA metrics from uptime ratio or downtime duration over any period.

      O M T

## How Uptime Percentage Is Calculated

Uptime measures how much of a monitoring window a service stayed available. SLA contracts express this as a percentage such as 99.9%, which translates to a fixed amount of allowed downtime over the period.

## Uptime Formula

 $$\text{uptime \%} = \frac{\text{total time} - \text{downtime}}{\text{total time}} \times 100$$ $$\text{downtime} = \text{total time} \times \left(1 - \frac{\text{uptime \%}}{100}\right)$$

Example: 43 minutes of downtime in 30 days equals 99.9002% uptime. A 99.9% SLA over 30 days allows about 43.2 minutes of downtime.

## Frequently Asked Questions

   **How much downtime is allowed for 99.9% uptime in 30 days?**

About 43.2 minutes. That is 0.1% of 30 days (43,200 minutes).

   **What is the difference between 99%, 99.9%, and 99.99%?**

Each extra nine reduces allowed downtime by a factor of ten. 99% allows 1% downtime, 99.9% allows 0.1%, and 99.99% allows 0.01%.

   **Can I enter uptime percentage instead of downtime?**

Yes. Switch input mode to enter uptime percentage and the calculator returns the equivalent downtime for your selected period.

   **Does planned maintenance count as downtime?**

That depends on your SLA definition. Some contracts exclude scheduled maintenance windows; others count all unavailable time.

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```