Uptime Calculator
Turn an uptime percentage into the downtime it actually allows — per day, week, month, quarter and year. Or enter real downtime to see the uptime you delivered. Runs entirely in your browser.
SLA uptime → allowed downtime
- Daily
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- Weekly
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- Monthly
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- Quarterly
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- Yearly
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Enter a percentage between 0 and 100.
Actual downtime → uptime %
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Downtime allowed by each SLA level
The "nines" of availability. Month and quarter use the average calendar length (a year of 365.2425 days divided by 12 and 4).
| Uptime | Daily | Weekly | Monthly | Quarterly | Yearly |
|---|---|---|---|---|---|
| 90% | 2h 23m 60s | 16h 47m 60s | 3d 1h 2m | 9d 3h 8m | 36d 12h 34m |
| 95% | 1h 12m | 8h 24m | 1d 12h 31m | 4d 13h 34m | 18d 6h 17m |
| 99% | 14m 24s | 1h 40m 48s | 7h 18m 17s | 21h 54m 52s | 3d 15h 39m |
| 99.5% | 7m 12s | 50m 24s | 3h 39m 9s | 10h 57m 26s | 1d 19h 49m |
| 99.9% | 1m 26s | 10m 5s | 43m 50s | 2h 11m 29s | 8h 45m 57s |
| 99.95% | 43s | 5m 2s | 21m 55s | 1h 5m 45s | 4h 22m 58s |
| 99.99% | 9s | 1m | 4m 23s | 13m 9s | 52m 36s |
| 99.999% | 864 ms | 6s | 26s | 1m 19s | 5m 16s |
What an uptime SLA really promises
An uptime percentage is a downtime budget. 99.9% sounds close to perfect, but it permits a 43-minute outage every single month — long enough to lose a morning of orders or miss a client launch. Each extra nine cuts the budget by a factor of ten, and each one costs more to deliver: redundancy, failover, and on-call staff.
Two details decide what a number is worth. First, how downtime is measured: many SLAs exclude scheduled maintenance, partial outages, or incidents shorter than a few minutes. Second, who measures it. A host's own dashboard sees its servers, not the DNS, certificate, or CDN failures that stop visitors reaching your site. An independent external check is the only way to know what customers actually experienced — and the only evidence you can take to a provider when you claim an SLA credit.
If you run sites for clients, the same maths applies in reverse: quote an uptime you can prove. The client site down triage checklistcovers what to do when the budget is being spent, and guides like502 Bad Gateway and503 Service Unavailableexplain the most common causes.
Measure the uptime you actually deliver
SitesRadar checks your site from outside your network, confirms every failure before alerting, and keeps an uptime history — free for one site.
Frequently asked questions
- How much downtime is 99.9% uptime?
- 99.9% uptime ("three nines") allows about 43 minutes 50 seconds of downtime per month, 10 minutes 5 seconds per week, and 8 hours 46 minutes per year.
- How much downtime is 99.99% uptime?
- 99.99% uptime ("four nines") allows about 4 minutes 23 seconds of downtime per month and 52 minutes 36 seconds per year.
- What does "five nines" mean?
- Five nines is 99.999% availability: about 26 seconds of downtime per month and 5 minutes 16 seconds per year. Three nines (99.9%) is roughly 8 hours 46 minutes per year, and four nines (99.99%) is about 52 minutes per year.
- What is the difference between an SLA and an SLO?
- An SLO (service level objective) is the internal target a team aims for, such as 99.95% monthly uptime. An SLA (service level agreement) is the contractual promise to customers, usually set slightly lower than the SLO, with credits or refunds if it is missed.
- How do you calculate uptime percentage?
- Uptime % = (total time − downtime) ÷ total time × 100. For example, 30 minutes of downtime in a 30-day month is (43,200 − 30) ÷ 43,200 × 100 = 99.93%.
- What uptime should a website SLA promise?
- Most hosting and SaaS providers promise 99.9% for standard plans and 99.95% to 99.99% for premium or redundant setups. A single server without failover realistically delivers around 99.5% to 99.9% once maintenance and incidents are included.
- Does scheduled maintenance count as downtime?
- It depends on the SLA. Many contracts exclude announced maintenance windows, so read the definition of downtime in the agreement, not just the percentage.
- How do I measure my real uptime?
- Use an external monitor that checks the site from outside your network on a fixed schedule and records every failure. Self-reported uptime from the server itself misses network, DNS and certificate failures.