Uptime & SLA Downtime Calculator
Calculate exactly how much downtime each SLA level allows. Enter an uptime percentage or a downtime budget to see the conversion. Used by DevOps teams, SREs, and IT managers to plan SLA commitments and estimate downtime costs.
Allowed Downtime at 99.9% Uptime
SLA Comparison Table
| SLA Level | Downtime / Year | Downtime / Month | Downtime / Week | Downtime / Day |
|---|---|---|---|---|
| 99% | 3d 15h 40m | 7h 18m | 1h 41m | 14m |
| 99.5% | 1d 19h 50m | 3h 39m | 50m | 7m |
| 99.9% | 8h 46m | 44m | 10m | 1m |
| 99.95% | 4h 23m | 22m | 5m | 43s |
| 99.99% | 53m | 4m | 1m | 9s |
| 99.999% | 5m | 26s | 6s | 1s |
What Does 99.9% Uptime Mean?
An uptime SLA (Service Level Agreement) of 99.9% — often called “three nines” — means your service is allowed a maximum of 8 hours and 46 minutes of downtime per year, or roughly 43 minutes per month. This is one of the most common SLA tiers offered by cloud providers, hosting companies, and SaaS platforms.
While 99.9% sounds nearly perfect, the allowed downtime can be significant for mission-critical applications. E-commerce sites, payment processors, and healthcare platforms often require 99.99% or higher to avoid revenue loss and user trust erosion.
Common SLA Uptime Tiers Compared
Different industries and service types require different levels of availability. Here is what each common SLA tier means in practical terms:
| SLA Level | Common Name | Downtime / Year | Downtime / Month | Typical Use Case |
|---|---|---|---|---|
| 99% | Two nines | 3d 15h 36m | 7h 18m | Internal tools, dev environments |
| 99.9% | Three nines | 8h 46m | 43m 50s | SaaS apps, business websites |
| 99.95% | Three and a half nines | 4h 23m | 21m 55s | E-commerce, customer portals |
| 99.99% | Four nines | 52m 36s | 4m 23s | Financial services, healthcare |
| 99.999% | Five nines | 5m 16s | 26s | Emergency services, critical infrastructure |
How Much Does Downtime Cost?
The cost of downtime varies dramatically by industry and company size. According to industry research, the average cost of IT downtime is estimated at $5,600 per minute for large enterprises. For small and mid-sized businesses, even a few hours of downtime can result in thousands of pounds in lost revenue, damaged reputation, and reduced customer trust.
Factors That Affect Downtime Cost
- Lost revenue — direct sales lost during outage
- Productivity loss — employees unable to work
- SLA penalties — contractual credits owed to customers
- Recovery costs — engineering time to diagnose and fix
- Reputation damage — customer churn and negative reviews
- Data loss — potential data corruption during unplanned outages
This is why monitoring your uptime continuously and catching issues early is critical. A proactive monitoring setup can reduce mean time to detect (MTTD) from hours to seconds.
Frequently Asked Questions
What is an SLA (Service Level Agreement)?
An SLA is a contract between a service provider and a customer that defines the expected level of service, including uptime guarantees, response times, and remedies (such as service credits) if those targets are not met. SLAs are standard in cloud computing, web hosting, and SaaS.
What is the difference between uptime and availability?
Uptime measures the total time a system is operational, while availability measures the percentage of time a system is accessible and functioning correctly. In practice, these terms are often used interchangeably, but availability also accounts for planned maintenance windows that may not count as downtime in an SLA.
How is uptime percentage calculated?
Uptime percentage is calculated as: (Total time - Downtime) / Total time x 100. For example, if a service was down for 43 minutes in a 30-day month (43,200 minutes), the uptime would be (43,200 - 43) / 43,200 x 100 = 99.9%.
What does “five nines” (99.999%) availability mean?
Five nines availability means a service can only be down for approximately 5 minutes and 16 seconds per year, or about 26 seconds per month. This level of availability is extremely difficult and expensive to achieve, typically requiring redundant infrastructure, automatic failover, and multi-region deployments.
How do I monitor my website uptime?
You can monitor website uptime using a service like Uptrue that checks your website at regular intervals (as frequently as every minute) from multiple locations. When your site goes down, you receive instant alerts via email, Slack, SMS, or webhook so you can respond quickly.
What is MTTR and MTTD?
MTTD (Mean Time to Detect) is the average time it takes to discover a problem. MTTR (Mean Time to Recover) is the average time it takes to restore service after a failure is detected. Reducing both metrics is key to maintaining high uptime percentages.
Does planned maintenance count against SLA uptime?
This depends on the specific SLA agreement. Many providers exclude scheduled maintenance windows from their uptime calculations, provided they give advance notice (typically 24-72 hours). Always check the fine print of your provider's SLA.
What uptime SLA should I offer my customers?
The right SLA depends on your infrastructure, budget, and customer expectations. Most SaaS platforms start with 99.9% and upgrade to 99.95% or 99.99% as they mature. Offering an SLA you cannot consistently meet will erode trust faster than not having one at all.
Monitor your uptime automatically
Stop calculating downtime manually. Let Uptrue track your uptime 24/7 and alert you the moment something goes wrong. Get started in under 2 minutes.
Start Monitoring Free