99.5% uptime SLA downtime calculator.
99.5% uptime, or two and a half nines of availability, allows 3h 39m 8s of downtime per month and 1d 19h 49m 44s per year.
two and a half nines
- downtime per day
- 7m 12s
- downtime per week
- 50m 24s
- downtime per month
- 3h 39m 8s
- downtime per year
- 1d 19h 49m 44s
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A month is 30.44 days and a year 365.24 days, their averages over the Gregorian calendar. Downtime is rounded down to the second.
Downtime to uptime calculator
Rough month? Enter the downtime of your service to calculate its uptime percentage, and see which SLA levels survived.
Downtime
Period
SLA levels met
- 99% missedmet
- 99.5% missedmet
- 99.9% missedmet
- 99.95% missedmet
- 99.99% missedmet
- 99.999% missedmet
- 99.9999% missedmet
- Uptime
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99.9315%
over a month
SLA uptime and downtime table
The nines of availability, from one nine (90% uptime) to six nines (99.9999%), and the downtime each SLA level allows.
| Uptime | Day | Week | Month | Quarter | Year |
|---|---|---|---|---|---|
| 90% One nine | 2h 24m | 16h 48m | 3d 1h 2m 54s | 9d 3h 8m 43s | 36d 12h 34m 55s |
| 95% One and a half nines | 1h 12m | 8h 24m | 1d 12h 31m 27s | 4d 13h 34m 21s | 18d 6h 17m 27s |
| 99% Two nines | 14m 24s | 1h 40m 48s | 7h 18m 17s | 21h 54m 52s | 3d 15h 39m 29s |
| 99.5% Two and a half nines | 7m 12s | 50m 24s | 3h 39m 8s | 10h 57m 26s | 1d 19h 49m 44s |
| 99.8% | 2m 52s | 20m 9s | 1h 27m 39s | 4h 22m 58s | 17h 31m 53s |
| 99.9% Three nines | 1m 26s | 10m 4s | 43m 49s | 2h 11m 29s | 8h 45m 56s |
| 99.95% Three and a half nines | 43s | 5m 2s | 21m 54s | 1h 5m 44s | 4h 22m 58s |
| 99.99% Four nines | 8s | 1m | 4m 22s | 13m 8s | 52m 35s |
| 99.999% Five nines | 864ms | 6s | 26s | 1m 18s | 5m 15s |
| 99.9999% Six nines | 86ms | 605ms | 2s | 7s | 31s |
How SLA uptime is calculated
The fine print behind the percentage: what an uptime SLA commits you to, how availability is measured, and what counts as downtime.
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SLA vs SLO vs SLI
A service level agreement (SLA) is the uptime you promise by contract, with service credits when you miss it. The service level objective (SLO) is the stricter target you keep to yourself, and the service level indicator (SLI) is what you actually measure.
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Uptime percentage formula
Uptime % = (total time − downtime) ÷ total time × 100. With 43 minutes of downtime in a 30-day month: (43,200 − 43) ÷ 43,200 × 100 = 99.90% uptime.
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Uptime monitoring interval
A 99.99% SLA allows 4m 22s of downtime per month, less than a single 5-minute check interval: the budget can be spent before the monitor notices. Phare checks your websites and APIs as often as every 30 seconds.
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Planned maintenance
Most SLAs leave maintenance out of the downtime, as long as it is announced in advance. Phare maintenance windows warn your users ahead of time and keep paused monitors out of your uptime reports.
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Composite SLA
Availability multiplies along the chain: an application that needs three services with a 99.9% SLA each cannot promise more than 99.7% uptime, over a day of downtime per year.
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The cost of high availability
Each extra nine divides your error budget, the downtime you can afford, by ten, and costs more than the last. At 99.99% uptime, 52m 35s per year is less than most teams need to notice, diagnose and fix a single incident.
Frequently asked questions
You could not find the answer to your question? Ask support.
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How much downtime does 99.5% uptime allow?
A 99.5% uptime SLA, or two and a half nines of availability, allows 7m 12s of downtime a day, 50m 24s a week, 3h 39m 8s a month, 10h 57m 26s a quarter and 1d 19h 49m 44s a year. Common on entry-level hosting plans, with room for an outage or two every month.
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What do “three nines” and “five nines” mean?
They count the nines in the uptime percentage: 99.9% is three nines of availability, 99.999% is five nines. A trailing 5 counts as half a nine, so 99.95% is three and a half nines. Each extra nine divides the allowed downtime by ten.
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How long is a month in an SLA?
It depends on the contract. This calculator uses the average Gregorian month of 30.44 days, so that twelve months make a year. Over a 30-day month, a 99.9% SLA allows 43m 12s of downtime, and 44m 38s over a 31-day month.
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Does planned maintenance count as downtime?
Usually not, as long as it is announced in advance and stays within the limits of the contract: check its notice period. Phare maintenance windows warn your users ahead of time and keep paused monitors out of your uptime reports.
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What is a good uptime SLA?
It depends on what an outage costs you. 99.9% uptime is the most common SLA of SaaS products, 99.99% is expected from the infrastructure other services depend on, and each extra nine costs more to reach than the last.
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What is the difference between uptime and availability?
Uptime is the time a service is running, availability is the share of time it can actually be used: a server can be up while the website it hosts returns errors. SLAs use both words for the same percentage, so read how the contract defines downtime.
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What happens when an SLA is missed?
The provider usually owes service credits, a discount on the next invoice that grows with the downtime. They are rarely automatic: most contracts expect the customer to claim them, with proof of the outage and within a deadline.
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Is 100% uptime possible?
Not for long. Hardware fails, certificates expire, a cloud region goes dark, and sooner or later it is DNS. That is why an SLA leaves an error budget rather than promise 100%.
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How do I measure the uptime of my website?
With an uptime monitor that checks it from several regions, often enough to catch short outages. Phare checks your websites and APIs as often as every 30 seconds, reports their uptime, and hosts your status page, with a free plan to get started.
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