What does an SLA calculator do?

It takes a service level agreement percentage, say 99.9%, and tells you the downtime that figure permits per day, week, month and year. Reach for it when you want to compare SLA levels side by side, settle on an availability target you can actually hit, or confirm a provider stayed inside what it promised.

How does the uptime calculator work?

Type in how long you were down and the window it fell within. The tool hands back your availability: uptime % = (period - downtime) / period x 100. Handy when you want to check the uptime figure your hosting or SaaS provider claims against reality.

How much downtime is 99.9% uptime?

A 99.9% SLA leaves room for 1 minute 26 seconds of downtime per day, 10 minutes 5 seconds per week, 43 minutes 50 seconds per month and 8 hours 46 minutes across a full year. Those figures use 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?

Add a nine and your downtime allowance drops tenfold. 99.9% buys you roughly 43 minutes 50 seconds a month; 99.99% gives you just 4 minutes 23 seconds. Earning that extra nine tends to mean redundancy, automated failover, and catching incidents far sooner than before.

What does "five nines" mean?

Five nines means 99.999% uptime, which works out to roughly 26 seconds of downtime a month or 5 minutes 16 seconds a year. That level belongs to carrier-grade telecom kit. You will almost never see it promised for an everyday web service.

How do I calculate an uptime percentage?

The formula is uptime % = (total period - downtime) / total period x 100. Say you lost 2 hours in a 30.44-day month, which is 730.5 hours: (730.5 - 2) / 730.5 x 100 = 99.726%.

Does scheduled maintenance count as downtime?

That comes down to the fine print. Plenty of providers leave announced maintenance windows out of the math, which means the headline percentage can read better than the availability you live with. Read the measurement window (monthly or yearly) and the exclusions list before you trust the number.

Is 100% uptime realistic?

No. Hardware dies, networks flap, deploys break, and that is why even the biggest cloud providers publish SLAs under 100%. A more honest goal: pick a target your architecture can hold, then spot and fix incidents quickly 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) commits to a percentage of availability. Run it through the SLA calculator above and you get the downtime budget that percentage allows. Go the other way, feed in real downtime, and the uptime calculator returns an availability percentage. Two formulas do all of it.

Allowed downtime is whatever slice of a period the SLA leaves unpromised: downtime = period x (1 - SLA / 100). Take a 99.9% SLA across a month: 730.5 hours x 0.001 = 0.7305 hours, or 43 minutes 50 seconds.

Going backwards uses the mirror of that: uptime % = (period - downtime) / period x 100. Lose two hours in a month and you get (730.5 - 2) / 730.5 x 100 = 99.726%.

The numbers here lean on calendar averages so they hold steady month to month: a month counts as 30.44 days (365.25 divided by 12) and a year as 365.25 days. Some providers measure against the real calendar month instead, which is why breaching an SLA in February can take a touch less downtime than in July. The gap is tiny, though it can matter once an SLA credit is at stake.

Reading an SLA: the fine print

The measurement window matters. Measure 99.9% by the month and you get 43 minutes 50 seconds each month. Measure the same 99.9% by the year and one outage of nearly 9 hours can pass, provided the rest of the year stays clean. Monthly windows bite harder, and that is what most SaaS providers run on.

Exclusions shrink the promise. Scheduled maintenance, force majeure, breakage from your own configuration, third-party failures: contracts routinely carve these out. The percentage you signed for covers only what remains after them.

An SLA is a refund policy, not a guarantee. Break it and you typically collect service credits, never the revenue or the trust the outage burned through. So teams measure their own availability rather than take the provider's reporting at face value, and a quick is-it-down check from outside your own network is where most incidents start.

Choosing a target you can keep

Each nine you add roughly multiplies the engineering bill: redundancy, failover, faster pipelines, on-call coverage. For a solo project, 99.5% is usually plenty. A paid product tends to promise 99.9%. Push past 99.99% and you are signing up for multi-region architecture and a team that responds in minutes, since the whole monthly budget is 4 minutes 23 seconds.

Whatever target you set, the budget is useless unless you notice when it starts draining. Detection eats into the same budget as the repair. Check every 30 seconds and you forfeit half a minute at most before the alert lands. Check every 5 minutes and one quiet outage can chew through an entire 99.99% monthly budget (4 minutes 23 seconds) before anyone is the wiser.

When an incident does hit, what users see counts every bit as much as your repair speed. A public status page answers the "is it just me?" question before the support queue fills up, and our error guides walk through the 502s and timeouts your visitors are staring at while you work.

Frequently asked questions

What does an SLA calculator do?

It takes a service level agreement percentage, say 99.9%, and tells you the downtime that figure permits per day, week, month and year. Reach for it when you want to compare SLA levels side by side, settle on an availability target you can actually hit, or confirm a provider stayed inside what it promised.
How does the uptime calculator work?

Type in how long you were down and the window it fell within. The tool hands back your availability: uptime % = (period - downtime) / period x 100. Handy when you want to check the uptime figure your hosting or SaaS provider claims against reality.
How much downtime is 99.9% uptime?

A 99.9% SLA leaves room for 1 minute 26 seconds of downtime per day, 10 minutes 5 seconds per week, 43 minutes 50 seconds per month and 8 hours 46 minutes across a full year. Those figures use 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?

Add a nine and your downtime allowance drops tenfold. 99.9% buys you roughly 43 minutes 50 seconds a month; 99.99% gives you just 4 minutes 23 seconds. Earning that extra nine tends to mean redundancy, automated failover, and catching incidents far sooner than before.
What does "five nines" mean?

Five nines means 99.999% uptime, which works out to roughly 26 seconds of downtime a month or 5 minutes 16 seconds a year. That level belongs to carrier-grade telecom kit. You will almost never see it promised for an everyday web service.
How do I calculate an uptime percentage?

The formula is uptime % = (total period - downtime) / total period x 100. Say you lost 2 hours in a 30.44-day month, which is 730.5 hours: (730.5 - 2) / 730.5 x 100 = 99.726%.
Does scheduled maintenance count as downtime?

That comes down to the fine print. Plenty of providers leave announced maintenance windows out of the math, which means the headline percentage can read better than the availability you live with. Read the measurement window (monthly or yearly) and the exclusions list before you trust the number.
Is 100% uptime realistic?

No. Hardware dies, networks flap, deploys break, and that is why even the biggest cloud providers publish SLAs under 100%. A more honest goal: pick a target your architecture can hold, then spot and fix incidents quickly enough to stay inside its downtime budget.

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