An uptime calculator converts an availability target such as 99.9% into the amount of downtime your service can tolerate, or calculates your actual realized uptime percentage after an incident. Select a standard SLA target to view error budgets, or input your outage duration to verify SLA compliance.
A calendar month varies by month length, so the actual downtime allowance differs for 28-, 29-, 30- and 31-day months:
44m 38s
Jan, Mar, May, Jul, Aug, Oct, Dec43m 11s
Apr, Jun, Sep, Nov41m 45s
February (Leap Year)40m 19s
February (Common Year)The Table of Nines illustrates allowed downtime per day, week, month, and year across standard availability tiers. A 99.9% availability target permits approximately 43 minutes 49 seconds of downtime per average month (30.4375 days):
| SLA Target | Daily | Weekly | Monthly (Avg 30.44d) | 30-Day Month | 31-Day Month | Yearly |
|---|---|---|---|---|---|---|
| 99.0% (Two Nines) | 14m 24s | 1h 40m 48s | 7h 18m 18s | 7h 12m | 7h 26m 24s | 3d 15h 39m |
| 99.5% | 7m 12s | 50m 24s | 3h 39m 09s | 3h 36m | 3h 43m 12s | 1d 19h 49m |
| 99.9% (Three Nines) | 1m 26s | 10m 04s | 43m 49s | 43m 12s | 44m 38s | 8h 45m 57s |
| 99.95% | 43s | 5m 02s | 21m 54s | 21m 36s | 22m 19s | 4h 22m 58s |
| 99.99% (Four Nines) | 8.64s | 1m 00s | 4m 23s | 4m 19s | 4m 28s | 52m 35s |
| 99.999% (Five Nines) | 0.86s | 6.05s | 26.3s | 25.9s | 26.8s | 5m 15s |
The standard SaaS SLA target. Complete daily, weekly, monthly and yearly breakdown with contract clauses.
High-availability cloud architecture. Sub-5-minute monthly downtime limits and multi-region failover tips.
Common cloud infrastructure SLA tier (AWS/Azure single-region multi-AZ).
Staging, batch processing, and non-critical developer services SLA analysis.
Mission-critical telecom, banking, and emergency services availability architecture.
Full SRE reference chart comparing 1 Nine through 6 Nines with downloadable cheat sheets.
To calculate actual availability, divide total operational seconds (total seconds in the period minus outage downtime seconds) by total seconds in the period, then multiply by 100. For example, if your service experienced 47 minutes (2,820 seconds) of downtime in a 30-day month (2,592,000 seconds): ((2,592,000 - 2,820) ÷ 2,592,000) × 100 = 99.891% availability. This breached a 99.9% SLA target (which permits a maximum of 43 minutes and 12 seconds in a 30-day month).
SLA downtime is calculated by multiplying the downtime fraction (1 - SLA%) by the total number of seconds in a given time period. Standard Site Reliability Engineering (SRE) practice uses an average month of 30.4375 days (365.25 days ÷ 12 = 2,629,800 seconds). For a 99.9% SLA (0.001 downtime fraction), this yields approximately 43 minutes 49 seconds of downtime per average month. A calendar month varies by month length, so the actual contractual allowance is different for 28-, 29-, 30- and 31-day months (ranging from 40m 19s in a 28-day February to 44m 38s in a 31-day month).
A 99.9% availability target permits approximately 43 minutes 49 seconds of downtime per average month (30.4375 days), or 8 hours and 45 minutes of downtime across a calendar year. Because calendar months vary by month length, the exact allowance is 43 minutes and 12 seconds for a 30-day month, and 44 minutes and 38 seconds for a 31-day month.
A 99.99% availability target (four nines) allows approximately 4 minutes and 23 seconds of downtime per average month (30.4375 days), or 52 minutes and 35 seconds per year. In a 30-day month, the allowance is 4 minutes and 19 seconds, while in a 31-day month it is 4 minutes and 28 seconds.
Most Enterprise Service Level Agreements (SLAs) evaluate uptime on a calendar-month billing cycle. If your contract specifies a 99.9% target, you have 44m 38s of error budget in January (31 days), 43m 12s in April (30 days), and 40m 19s in February (28 days). Uptara tracks both calendar-month compliance and rolling 30-day windows to prevent contract breaches.
Uptara continuously checks endpoints across multi-region edge nodes (every 3 minutes on the Free tier with 10 free monitors, down to 30 seconds on Pro plans). When downtime or latency degradation occurs, multi-region quorum consensus verifies the failure and immediately triggers WhatsApp, Slack, PagerDuty, and webhook alerts to minimize MTTR.
Explore connected platform capabilities, in-depth engineering guides, and interactive developer utilities.
Mathematical formulas, MTTR/MTTD definitions, 99.9% vs 99.99% availability calculations, and maintenance rules.
Engineering guide to the SLI/SLO/SLA hierarchy, the Table of Nines, and error budget burn rates.
A mathematically grounded framework for time-based vs request-based availability and incident lifecycle.
Free reliability tools for developers and engineering teams detecting downtime, tracking response latency, and calculating real SLAs with Uptara.