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Uptime Calculator — Calculate Downtime & Availability

Calculate how much downtime an uptime target allows, or find your uptime percentage from actual downtime. It runs in your browser, needs no account, and sends nothing anywhere.

Open the calculator Compare common targets

The calculator

The calculator needs JavaScript. Turn it on in your browser to use it. The table of common targets below works without it.

What do you want to calculate?

Uptime → downtime Downtime → uptime

Pick an uptime target

99% 99.5% 99.9% 99.95% 99.99% 99.999%

Or enter your own uptime, in %

From 0 to 100, with up to 6 digits after the dot.

A day is 24 hours, a week is 7 days, a month is 30 days, and a year is 365 days. These are calculation conventions: a calendar month has 28 to 31 days, and a leap year has 366. For another length, use “Other number of days” in the second calculation. The figures are what a target allows in theory. They are not measured uptime, and they do not show whether a contract was met.

Common uptime targets compared.

How much downtime each target allows. A day is 24 hours, a month is 30 days, and a year is 365 days. The targets are examples for comparison. They are not commitments made by UptimeWire.

Downtime allowed by common uptime targets, for a day, a week, a 30-day month, and a 365-day year
Uptime target	Per day	Per week	Per month (30 days)	Per year (365 days)
99%	14 minutes 24 seconds	1 hour 40 minutes 48 seconds	7 hours 12 minutes	3 days 15 hours 36 minutes
99.5%	7 minutes 12 seconds	50 minutes 24 seconds	3 hours 36 minutes	1 day 19 hours 48 minutes
99.9%	1 minute 26.4 seconds	10 minutes 4.8 seconds	43 minutes 12 seconds	8 hours 45 minutes 36 seconds
99.95%	43.2 seconds	5 minutes 2.4 seconds	21 minutes 36 seconds	4 hours 22 minutes 48 seconds
99.99%	8.64 seconds	1 minute 0.5 seconds	4 minutes 19.2 seconds	52 minutes 33.6 seconds
99.999%	864 milliseconds	6.05 seconds	25.92 seconds	5 minutes 15.4 seconds

Seconds are rounded for display only, so 99.99% over a week (60.48 seconds) reads as 1 minute 0.5 seconds. Each extra “nine” cuts the allowance by a factor of ten.

How uptime and downtime relate.

What is uptime?

Uptime is the share of a chosen period during which a website or service counts as available. It is written as a percentage. The rest of the period is downtime. The glossary covers the details in Uptime and Downtime.

How is uptime calculated?

Both directions use the same relation between the period and the downtime:

Downtime = Period × (1 − Uptime ÷ 100)
Uptime (%) = (Period − Downtime) ÷ Period × 100

Take a 30-day month, which has 43,200 minutes, and an uptime target of 99.9%. The allowed downtime is 0.1% of 43,200 minutes, which is 43.2 minutes, or 43 minutes 12 seconds.

Going the other way, suppose the site was down for 18 minutes in the same month. Uptime is (43,200 − 18) ÷ 43,200 × 100, which is 99.958333%.

How much downtime does 99.9% allow?

About 43 minutes 12 seconds in a 30-day month, 10 minutes 4.8 seconds in a week, and 8 hours 45 minutes 36 seconds in a 365-day year. At 99.99% the month allowance falls to 4 minutes 19.2 seconds. The table above shows the other common targets.

Uptime and SLA are not the same thing

An SLA is a contract. It says how availability is measured, which periods are excluded (planned maintenance, for example), and what happens when a target is missed. A calculation like this one shows what a percentage means in time. It cannot show that an SLA was met or broken, because that depends on the wording of the agreement.

Why continuous monitoring matters

This calculator works with numbers you already have. It does not look at any website. Knowing the real figure takes repeated checks that record each result, and an alert when something fails. UptimeWire monitors each website URL you add for uptime, SSL certificate, domain expiration, and DNS resolution, at an interval your plan allows. A check at a fixed interval can still miss an outage shorter than the interval, and a page that answers is not proof that every function works. See what UptimeWire checks or how it works.

Questions about the calculator.

Why does it use 30 days for a month?

Because it needs one fixed length to make results comparable. A calendar month has 28 to 31 days. If your agreement or report uses a calendar month, choose “Other number of days” in the second calculation and enter 28, 29, 30, or 31.

Is the result my website’s real uptime?

No. The first calculation shows what a target allows in theory, and the second turns a downtime figure you provide into a percentage. Neither measures a website.

Does 99.9% uptime mean an SLA was met?

Not by itself. An SLA is defined by its contract: how availability is measured, what is excluded, and over which period. Read the agreement.

Are my numbers sent anywhere?

No. The calculation happens in your browser. If you copy the link, it contains only the numbers of the calculation, so anyone who opens it sees the same inputs.

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Want the real number for your website?

A calculator turns percentages into minutes. UptimeWire checks your website at an interval your plan allows, keeps every result, and alerts you. Every website includes uptime, SSL certificate, domain expiration, and DNS resolution checks.

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