Uptime SLA Calculator
Convert an uptime percentage into the downtime it allows per day, week, month, quarter and year, or enter downtime to get the percentage. For example, 99.9% allows about 43 minutes a month.
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99.9% uptime allows 8h 45m 58s of downtime a year
43m 50s a month · 1m 26s a day
| Period | Allowed downtime |
|---|---|
| Day | 1m 26s |
| Week | 10m 5s |
| Month (30.44 days) | 43m 50s |
| Quarter (91.31 days) | 2h 11m 29s |
| Year (365.25 days) | 8h 45m 58s |
Examples
A hosting contract promises 99.9%
0.1% of a 30.44-day month is 43 minutes 50 seconds. A single 1-hour outage in that month breaks the SLA, so you can claim the credit the contract offers.
Your SaaS had a 2-hour outage
Over a 365.25-day year, 2 hours down is about 99.977% uptime. Over a single 30-day month it is about 99.72%, below a 99.9% monthly target.
Choosing between 99.9% and 99.99%
99.9% allows 8 hours 46 minutes a year, enough for a few incidents and a planned upgrade. 99.99% allows 52 minutes 36 seconds a year, which usually needs redundant servers and automatic failover.
Checking a status page claim
A provider showing 99.95% over 90 days was down about 1 hour 5 minutes in that period (0.05% of 129,600 minutes is 64.8 minutes).
How allowed downtime is calculated
Allowed downtime = (1 - availability % / 100) x period length
Subtract the availability from 100% to get the share of time the service may be down, then multiply by the length of the period. A day is 86,400 seconds.
This calculator uses an average month of 30.44 days (365.25 / 12) and a 365.25-day year, so leap years are averaged in. A specific calendar month of 28 or 31 days allows slightly less or more.
To go the other way, uptime % = (1 - downtime / period length) x 100.
Uptime percentage to allowed downtime
| Availability | Per day | Per month (30.44 days) | Per year (365.25 days) |
|---|---|---|---|
| 90% | 2h 24m | 3d 1h 3m | 36d 12h 36m |
| 95% | 1h 12m | 1d 12h 31m | 18d 6h 18m |
| 99% | 14m 24s | 7h 18m 20s | 3d 15h 39m |
| 99.5% | 7m 12s | 3h 39m 10s | 1d 19h 49m |
| 99.9% | 1m 26s | 43m 50s | 8h 45m 58s |
| 99.95% | 43s | 21m 55s | 4h 22m 59s |
| 99.99% | 8.6s | 4m 23s | 52m 36s |
| 99.999% | 0.86s | 26s | 5m 16s |
Common SLA mistakes
Promising nines you cannot measure
99.99% allows about 4 minutes a month. If you check every 5 or 15 minutes, a short outage can start and end between checks, so you cannot prove you met that target. Match the promise to how often you check.
Not defining the month
A 28-day February and a 31-day month allow different downtime at the same percentage. Say in the SLA whether it is measured per calendar month and how partial minutes count.
Forgetting planned maintenance
If maintenance windows count as downtime, a single long upgrade can use a whole month's budget. State clearly whether scheduled maintenance is excluded and how much notice you give.
Multiplying dependencies
A service that needs three components, each at 99.9%, has an upper bound of about 99.7% when any one of them failing takes it down. Your SLA cannot be higher than the chain it depends on.
Check something else
- Downtime Cost CalculatorEstimate what an outage costs in lost revenue and staff time, in USD, MYR, SGD, EUR, GBP and more.
- Website Down CheckerCheck if a website is down for everyone or just you, with status code, response time and final URL.
- Website Response Time TestMeasure how long a website takes to respond, split into DNS, connect, TLS, server wait and download.
- Cron Job Heartbeat TesterGet a temporary heartbeat URL and watch pings from your cron job or script arrive live.
Frequently asked questions
How much downtime is 99.9% uptime?
About 1 minute 26 seconds a day, 43 minutes 50 seconds a month and 8 hours 46 minutes a year, using a 30.44-day month and a 365.25-day year.
How much downtime is 99.99% uptime?
About 8.6 seconds a day, 4 minutes 23 seconds a month and 52 minutes 36 seconds a year.
What uptime should a small business website aim for?
99.9% is a common, realistic target for a site on a single good host. Going beyond it usually means redundant servers in more than one place. What matters most is finding out quickly when the site is down, so outages stay short.
Why do different calculators give slightly different numbers?
They use different period lengths: a 30-day or 31-day month, or a 365-day year instead of 365.25. This calculator states its assumptions (30.44-day month, 365.25-day year) so you can compare.
Can monitoring prove I met my SLA?
Monitoring shows when checks failed, which is good evidence, but it can only see what it checks. With a check every 5 minutes, an outage shorter than that can go unseen. For tight SLAs, check as often as you can and keep the incident history.
Protect your downtime budget
The fastest way to stay inside an SLA is to find out about outages before your customers do. TinyPing checks every 5 minutes and alerts you when:
- the site returns an error or times out
- the domain stops resolving or HTTPS breaks
- the site recovers, so you know how long it was down
US$6.99 a month or US$47 a year per 50 monitors, team members free. 7-day free trial, no card needed.
Want alerts in team chat? Follow the guide for Slack or Google Chat.