SLA Uptime Calculator
What does 99.9% actually allow? Turn an uptime target into allowed downtime per day, week, month and year, turn the downtime you had into the uptime you achieved, or work out availability from MTBF and MTTR. Every result shows its formula, and the month length is yours to set. If you are checking the Microsoft 365 outage that began on 12 November 2026 against Microsoft's SLA, read our Microsoft 365 outage briefing and use the Microsoft 365 example below.
What do you want to work out?
28 to 31. February has 28 (29 in a leap year); November has 30.
For example 99.9 or 99.95.
The nines: allowed downtime
Month = 30 days (43,200 minutes); year = 365 days.
| Uptime | Per day | Per week | Per month | Per year |
|---|---|---|---|---|
| 99% | 14 min 24 s | 1 h 40 min 48 s | 7 h 12 min | 3 d 15 h 36 min |
| 99.5% | 7 min 12 s | 50 min 24 s | 3 h 36 min | 1 d 19 h 48 min |
| 99.9% | 1 min 26 s | 10 min 5 s | 43 min 12 s | 8 h 45 min 36 s |
| 99.95% | 43.2 s | 5 min 2 s | 21 min 36 s | 4 h 22 min 48 s |
| 99.99% | 8.64 s | 1 min | 4 min 19 s | 52 min 34 s |
| 99.999% | 0.86 s | 6.05 s | 25.92 s | 5 min 15 s |
Microsoft 365 example (30-day month)
In Microsoft's Service Level Agreement for Microsoft Online Services (WW), November 1, 2026, Exchange Online, Microsoft Teams, SharePoint Online and OneDrive for work or school earn a service credit when monthly uptime falls below these thresholds. The minutes show how long a whole-tenant outage (every user down) would have to last to cross each one:
| Uptime below | Credit | Whole-tenant outage longer than |
|---|---|---|
| 99.9% | 25% of that service's monthly fees | 43.2 min (43 min 12 s) |
| 99% | 50% of that service's monthly fees | 432 min (7 h 12 min) |
| 95% | 100% of that service's monthly fees | 2,160 min (1 d 12 h) |
Microsoft measures these services in user-minutes, so an outage that hits only some users has to last longer to cross a threshold, and each service has its own definition of downtime. Microsoft 365 Copilot uses different tiers (below 99.5%) measured on failed prompts, not minutes. Credits are not automatic: you file a claim and Microsoft decides. This is an estimate, not advice. Read 2026-11-13.
The nines table for your month length, plus any results above, ready for a runbook, an SLA review or a vendor conversation.
TL;DRWhat this calculator does
5 points
- Enter an uptime target such as 99.9% and see the downtime it allows per day, week, month and year, with a table of the common "nines" from 99% to 99.999%.
- Month length is an input (28 to 31 days), because 99.9% allows 43.2 minutes in a 30-day month but 40.32 minutes in February.
- Enter incidents (minutes or hours, with optional start times so overlapping windows count once) to get the uptime you actually achieved and how much downtime budget is left.
- Work out availability from MTBF and MTTR with A = MTBF / (MTBF + MTTR). Every result shows the formula used. Results are estimates, not advice: each provider defines uptime in its own SLA.
- Free to use, signed out too. Everything runs in your browser and nothing is sent to us. Markdown and CSV exports of the table are available with a paid plan.
Frequently asked questions
How much downtime does 99.9% uptime allow?
99.9% ("three nines") allows 0.1% of the period as downtime: about 1 minute 26 seconds per day, 10 minutes 5 seconds per week, 43.2 minutes in a 30-day month and 8 hours 45 minutes 36 seconds in a 365-day year. In a 28-day February it is 40.32 minutes, and in a 31-day month 44.64 minutes.
How do I calculate allowed downtime from an SLA percentage?
Multiply the minutes in the period by (100 minus the uptime percentage) and divide by 100. A 30-day month has 30 x 24 x 60 = 43,200 minutes, so 99.95% allows 43,200 x 0.05 / 100 = 21.6 minutes. The calculator does this for a day, a week, your month length and a year.
How do I calculate uptime percentage from downtime?
Subtract the downtime minutes from the minutes in the period, divide by the minutes in the period and multiply by 100. One hour down in a 30-day month gives (43,200 - 60) / 43,200 x 100 = 99.861%, which misses a 99.9% target. If two alerts cover the same outage, count the overlapping time once: the calculator merges overlapping incident windows when you enter start times.
What is the difference between 99.9%, 99.99% and 99.999% uptime?
Each extra nine cuts the allowed downtime by a factor of ten. Per 365-day year: 99.9% allows about 8.76 hours, 99.99% about 52.56 minutes and 99.999% about 5.26 minutes. Per 30-day month: 43.2 minutes, 4.32 minutes and about 26 seconds.
How do you calculate availability from MTBF and MTTR?
Availability = MTBF / (MTBF + MTTR), where MTBF is the mean time between failures and MTTR is the mean time to repair, in the same unit. A system that runs 999 hours between failures and takes 1 hour to restore is available 999 / 1,000 = 99.9% of the time. It is a long-run planning average, not a contractual SLA figure.
Does an SLA measure uptime the same way as this calculator?
Not always. This calculator uses wall-clock time for the whole service. Many SLAs exclude planned maintenance, measure per user or per request, or define downtime narrowly. Microsoft 365, for example, measures Exchange Online, Teams, SharePoint and OneDrive in user-minutes per calendar month. Check the definitions in your provider's SLA before relying on a number.
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