What does an SLA calculator do?

An SLA calculator converts a service level agreement percentage such as 99.9% into the downtime it allows per day, week, month and year. Use it to compare SLA levels, to set a realistic availability target, or to check whether a provider stayed inside its promise.

How does the uptime calculator work?

Enter your measured downtime and the period it happened in, and the uptime calculator returns the availability percentage: uptime % = (period - downtime) / period x 100. Use it to verify the uptime your hosting or SaaS provider reports.

How much downtime is 99.9% uptime?

With a 99.9% SLA the service may be down for 1 minute 26 seconds per day, 10 minutes 5 seconds per week, 43 minutes 50 seconds per month and 8 hours 46 minutes per year (using calendar averages: a month of 30.44 days and a year of 365.25 days).

What is the difference between 99.9% and 99.99% uptime?

Each extra nine cuts the allowed downtime by 10 times. 99.9% allows about 43 minutes 50 seconds of downtime per month, while 99.99% allows only 4 minutes 23 seconds. Reaching that next nine usually requires redundancy, automated failover and much faster incident detection.

What does "five nines" mean?

Five nines is 99.999% uptime: about 26 seconds of downtime per month, or 5 minutes 16 seconds per year. It is the availability class associated with carrier-grade telecom systems and is rarely offered for ordinary web services.

How do I calculate an uptime percentage?

Uptime % = (total period - downtime) / total period x 100. For example, 2 hours of downtime in a 30.44-day month (730.5 hours) gives (730.5 - 2) / 730.5 x 100 = 99.726%.

Does scheduled maintenance count as downtime?

It depends on the SLA fine print. Many providers exclude announced maintenance windows from the calculation, so the marketed percentage can look better than the availability you actually experience. Always check the measurement window (monthly or yearly) and the exclusions list.

Is 100% uptime realistic?

No. Hardware fails, networks flap and deploys go wrong, so even the largest cloud providers publish SLAs below 100%. The realistic goal is to choose a target your architecture can sustain, then detect and resolve incidents fast enough to stay inside its downtime budget.

Free tool

SLA & Uptime Calculator

A free SLA calculator and uptime calculator: turn 99.9% into real minutes of allowed downtime, or convert an outage into the uptime percentage it cost you.

SLA to allowed downtime

Enter an uptime percentage to see the downtime budget it leaves you.
Uptime SLA
%

Show as

Per day
1m 26s

Per week
10m 5s

Per month
43m 50s

Per quarter
2h 11m 29s

Per year
8h 45m 58s

Month = 30.44 days, year = 365.25 days (calendar averages).
Revenue at risk (optional)
$

Revenue at risk per month
$0

Revenue at risk per year
$0

Assumes revenue is spread evenly across the period, so every minute of downtime costs the same.
Measured downtime to uptime

Had an outage? See what it did to your uptime percentage.
Total downtime

Over a period of

Resulting uptime

99.9977%

That is within a 99.9% SLA budget for this period.

Against common SLA budgets

99.5% budget
0.5% used

99.9% budget
2.3% used

99.99% budget
23% used

How much of each SLA's downtime allowance this outage consumes.

At 99.9%, your site can be down 43m 50s every month with nobody telling you. Pulsetic checks as often as every 30 seconds and alerts you the moment it happens.

The table of nines

Allowed downtime for every common SLA level.

Uptime SLA	Per day	Per week	Per month	Per year
90%	2h 24m 0s	16h 48m 0s	3d 1h 3m 0s	36d 12h 36m 0s
95%	1h 12m 0s	8h 24m 0s	1d 12h 31m 30s	18d 6h 18m 0s
98%	28m 48s	3h 21m 36s	14h 36m 36s	7d 7h 19m 12s
99%	14m 24s	1h 40m 48s	7h 18m 18s	3d 15h 39m 36s
99.5%	7m 12s	50m 24s	3h 39m 9s	1d 19h 49m 48s
99.8%	2m 53s	20m 10s	1h 27m 40s	17h 31m 55s
99.9%	1m 26s	10m 5s	43m 50s	8h 45m 58s
99.95%	43.2s	5m 2s	21m 55s	4h 22m 59s
99.99%	8.64s	1m 0s	4m 23s	52m 36s
99.995%	4.32s	30.24s	2m 11s	26m 18s
99.999%	0.86s	6.05s	26.3s	5m 16s
99.9999%	0.09s	0.6s	2.63s	31.56s

Click any row to load that SLA level into the calculator above.

How the uptime calculation works

An SLA (service level agreement) promises a percentage of availability. The SLA calculator above converts that percentage into the downtime budget it allows, and the uptime calculator direction converts measured downtime back into an availability percentage. The same two formulas power both.

Allowed downtime is the share of a period that the SLA does not promise: downtime = period x (1 - SLA / 100). For a 99.9% SLA over a month, that is 730.5 hours x 0.001 = 0.7305 hours, which is 43 minutes 50 seconds.

The reverse direction works the same way: uptime % = (period - downtime) / period x 100. Two hours of downtime in a month gives (730.5 - 2) / 730.5 x 100 = 99.726%.

This calculator uses calendar averages so the numbers stay consistent across the year: a month is 30.44 days (365.25 divided by 12) and a year is 365.25 days. Some providers measure against the actual calendar month instead, so a February SLA breach can need slightly less downtime than a July one. The differences are small, but worth knowing when an SLA credit is on the line.

Reading an SLA: the fine print

The measurement window matters. 99.9% measured monthly allows 43 minutes 50 seconds each month. The same 99.9% measured yearly allows one single outage of almost 9 hours, as long as the rest of the year is clean. Monthly windows are stricter and are what most SaaS providers use.

Exclusions shrink the promise. Scheduled maintenance, force majeure, problems caused by your own configuration and third-party failures are commonly excluded. The percentage in the contract only covers what is left.

An SLA is a refund policy, not a guarantee. Breaching it usually earns you service credits, not the revenue or trust an outage cost. That is why teams track their real availability themselves instead of relying on the provider's own reporting, and why a quick is-it-down check from outside your own network is the first step of any incident.

Choosing a target you can keep

Every extra nine costs roughly an order of magnitude more engineering: redundancy, failover, faster pipelines, on-call coverage. A solo project is often fine targeting 99.5%. A paid product typically promises 99.9%. Going beyond 99.99% means multi-region architecture and a team that can respond in minutes, because the entire monthly budget is 4 minutes 23 seconds.

Whatever the target, the budget only helps if you know when it starts burning. Detection time counts against the same budget as repair time: with 30-second checks you lose at most half a minute before the alert fires, while with 5-minute checks a single undetected outage can burn through an entire 99.99% monthly budget (4 minutes 23 seconds) before anyone knows.

And when an incident does land, what users see matters as much as how fast you fix it: a public status page answers "is it just me?" before support tickets pile up, and our error guides explain the 502s and timeouts your visitors are staring at in the meantime.

Frequently asked questions

What does an SLA calculator do?

An SLA calculator converts a service level agreement percentage such as 99.9% into the downtime it allows per day, week, month and year. Use it to compare SLA levels, to set a realistic availability target, or to check whether a provider stayed inside its promise.
How does the uptime calculator work?

Enter your measured downtime and the period it happened in, and the uptime calculator returns the availability percentage: uptime % = (period - downtime) / period x 100. Use it to verify the uptime your hosting or SaaS provider reports.
How much downtime is 99.9% uptime?

With a 99.9% SLA the service may be down for 1 minute 26 seconds per day, 10 minutes 5 seconds per week, 43 minutes 50 seconds per month and 8 hours 46 minutes per year (using calendar averages: a month of 30.44 days and a year of 365.25 days).
What is the difference between 99.9% and 99.99% uptime?

Each extra nine cuts the allowed downtime by 10 times. 99.9% allows about 43 minutes 50 seconds of downtime per month, while 99.99% allows only 4 minutes 23 seconds. Reaching that next nine usually requires redundancy, automated failover and much faster incident detection.
What does "five nines" mean?

Five nines is 99.999% uptime: about 26 seconds of downtime per month, or 5 minutes 16 seconds per year. It is the availability class associated with carrier-grade telecom systems and is rarely offered for ordinary web services.
How do I calculate an uptime percentage?

Uptime % = (total period - downtime) / total period x 100. For example, 2 hours of downtime in a 30.44-day month (730.5 hours) gives (730.5 - 2) / 730.5 x 100 = 99.726%.
Does scheduled maintenance count as downtime?

It depends on the SLA fine print. Many providers exclude announced maintenance windows from the calculation, so the marketed percentage can look better than the availability you actually experience. Always check the measurement window (monthly or yearly) and the exclusions list.
Is 100% uptime realistic?

No. Hardware fails, networks flap and deploys go wrong, so even the largest cloud providers publish SLAs below 100%. The realistic goal is to choose a target your architecture can sustain, then detect and resolve incidents fast enough to stay inside its downtime budget.

Know the moment your downtime budget starts burning

2-minute setup · Cancel any time
Create Free Account

Your Dashboard

No credit card needed