SLA & Uptime Calculator - Downtime per 99.9%
Free SLA uptime calculator. Enter any target (99%, 99.9%, 99.99%) to see allowed downtime per day, month and year. Instant results, no signup.
- days reporting: 9s downtime
- weeks reporting: 1m downtime
- months reporting: 4m 19s downtime
- years reporting: 52m 34s downtime
All calculations assume continuous 24/7 availability requirements.
Understanding Uptime SLA
Service Level Agreements (SLAs) define the expected performance and availability of your services. Understanding uptime percentages and their corresponding downtime allowances is crucial for maintaining customer trust and meeting compliance requirements.
Common SLA tiers include 99.9% (three nines), 99.99% (four nines), and 99.999% (five nines), each representing different levels of reliability. For example, 99.9% uptime allows for 8.77 hours of downtime per year, while 99.99% allows only 52.6 minutes annually.
This calculator helps you understand the real-world impact of your SLA commitments and plan for capacity, incident response, and stakeholder expectations.
From an SLA target to a measured number
A target is only half of it — the other half is measuring whether you hit it. Once you have picked a tier, openstatus uptime monitoring tracks the actual figure from 28 regions, and a public status page reports it back to the customers the SLA was written for.
Not sure which number you are agreeing to? SLA vs SLO vs SLI covers why your internal target should be stricter than the promise you publish.
Frequently asked questions
What is an uptime SLA?
An uptime SLA (Service Level Agreement) is a commitment between a service provider and a customer that guarantees a specific percentage of uptime over a given period. For example, a 99.9% SLA means the service can be down for no more than 8 hours and 45 minutes per year.
How much downtime does 99.9% uptime allow?
99.9% uptime (three nines) allows approximately 8 hours and 45 minutes of downtime per year, 43 minutes per month, 10 minutes per week, or 1 minute and 26 seconds per day.
How is SLA uptime calculated?
Uptime % = ((Total time − Downtime) / Total time) × 100.
For example, if your service was down for 1 hour in a 30-day month (720 hours), your uptime is ((720 − 1) / 720) × 100 = 99.86%. The subtlety is what counts as downtime in the first place — partial degradation, a single failing region, or a slow-but-responding endpoint may or may not be chargeable depending on how your agreement defines availability.
What are common SLA tiers?
Common tiers are 99.9% (three nines) allowing 8h 45m of downtime a year, 99.99% (four nines) allowing 52m 35s a year, and 99.999% (five nines) allowing only 5m 15s a year. Most cloud providers publish between 99.9% and 99.99%.
What is the difference between 99.9% and 99.99% uptime?
The difference is larger than one digit suggests: 99.9% allows about 8 hours 45 minutes of downtime per year, while 99.99% allows only about 52 minutes. That extra nine cuts your allowed downtime by roughly 10×, and it usually requires redundant infrastructure and automated failover rather than simply more careful operations.
What is a good SLA?
For most SaaS products, 99.9% is the right public commitment. It allows 43 minutes of downtime a month — enough room to deploy, patch, and recover from an incident without writing refund cheques. 99.99% is a commitment to redundant infrastructure and automated failover, not just a bigger number, and you should only publish it once you can prove you already hit it.
The best SLA is the one slightly below what you consistently achieve. See SLA vs SLO vs SLI for how to set the internal target that gives you that margin.
Is uptime measured monthly or yearly?
Almost always monthly, because that is the billing period service credits attach to. The distinction matters more than it looks: a single 5-hour outage is 99.94% measured over a year, but 99.3% measured over the month it happened in. A yearly window can hide an outage that a monthly window turns into a breach — check which one your agreement specifies before committing to a tier.