99.9% uptime allows 43 minutes 12 seconds of downtime in an exact 30-day month and 8 hours 45 minutes 36 seconds in a 365-day year.
Enter any target for an immediate conversion, or use reverse, comparison, and error-budget modes for deeper analysis.
Calculations run locally in your browser. Period conventions and rounding are stated below.
Availability target
Allowed downtime
99.9% allows 43 minutes 12 seconds per fixed 30-day month.
Per hour-
Per day (24 hours)-
Per week (7 days)-
Per fixed 30-day month-
Per fixed 90-day quarter-
Per 365-day year-
Results are ready.
Downtime to required uptime
Enter downtime and the full measurement period. The result is the availability that downtime represents.
4 hours in 30 days = 99.4444% uptime.
(2,592,000 - 14,400) ÷ 2,592,000 × 100
Compare SLA targets
Choose at least two targets. The same fixed periods are used for every row.
Allowed downtime by target using fixed periods
Target
Day
Week
30 days
90 days
365 days
Advanced error-budget calculator
Allowed downtime-
Actual availability-
Budget remaining-
Budget consumption ratio-
Failure-rate burn rate-
Compliance status-
Important: burn rate = observed failure rate ÷ sustainable failure rate. Above 1× predicts a future SLO miss if that rate is sustained; it does not by itself prove the current SLA window has already been breached. Budget consumption ratio compares failures already observed with the full compliance-period allowance.
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Methodology and trust
Period constants
1 day = 86,400 seconds; week = 7 days; fixed month = 28, 30, or 31 days; fixed quarter = 90 days; common year = 365 days. The average calendar month is 365.2425 ÷ 12 days. Exact dates use elapsed UTC midnights with the end date exclusive.
Rounding
Calculations use unrounded floating-point seconds. Durations display to 0.01 second when useful; percentages display up to six decimal places. A leap year is only included when exact dates span February 29; the fixed year remains 365 days.
What counts
Time mode treats entered downtime as fully unavailable. Request mode uses failed eligible events and can better represent partial outages. Maintenance, degraded service, exclusions, and weighting are included only if you include them in the entered figures.
500 failed of 1,000,000 events at 99.9% → 1,000 allowed failures, 50% consumed, 0.5× burn rate.
Availability “nines” quick-reference matrix
All monthly values below use an exact 30-day month, the quarter uses 90 days, and the year uses 365 days. The current basic-calculator target is highlighted when it matches a row.
Allowed downtime by availability target and fixed reporting period
Target
Day
Week
30-day month
90-day quarter
365-day year
99% two nines
14m 24s864 seconds
1h 40m 48s6,048 seconds
7h 12m25,920 seconds
21h 36m77,760 seconds
3d 15h 36m315,360 seconds
99.5%
7m 12s432 seconds
50m 24s3,024 seconds
3h 36m12,960 seconds
10h 48m38,880 seconds
1d 19h 48m157,680 seconds
99.9% three nines
1m 26.4s86.4 seconds
10m 4.8s604.8 seconds
43m 12s2,592 seconds
2h 9m 36s7,776 seconds
8h 45m 36s31,536 seconds
99.95%
43.2s43.2 seconds
5m 2.4s302.4 seconds
21m 36s1,296 seconds
1h 4m 48s3,888 seconds
4h 22m 48s15,768 seconds
99.99% four nines
8.64s8.64 seconds
1m 0.48s60.48 seconds
4m 19.2s259.2 seconds
12m 57.6s777.6 seconds
52m 33.6s3,153.6 seconds
99.999% five nines
0.864s0.864 seconds
6.048s6.048 seconds
25.92s25.92 seconds
1m 17.76s77.76 seconds
5m 15.36s315.36 seconds
99.9999% six nines
0.0864s0.0864 seconds
0.6048s0.6048 seconds
2.592s2.592 seconds
7.776s7.776 seconds
31.536s31.536 seconds
How to calculate availability and error budgets
Allowed downtime from a target
period × (1 - target ÷ 100). At 99.9%, the unavailable fraction is 0.001, so 2,592,000 seconds × 0.001 = 2,592 seconds in 30 days.
Actual uptime from downtime
(period - downtime) ÷ period × 100. Use the same units for both values. This measures observed availability; it does not decide which incidents a contract excludes.
How error budgets work
A time budget is allowed downtime. A request budget is eligible events × (1 - SLO). Consumption ratio is observed bad time or events divided by that full-period allowance. True burn rate instead divides the observed lookback failure rate by the SLO's sustainable failure rate.
SLA, SLO, and SLI
An SLI is the measured reliability signal, such as successful requests ÷ eligible requests. An SLO is the target for that signal. An SLA is an agreement that may attach remedies and define different measurement or exclusion rules.
Contractual exclusions
Planned maintenance, customer-caused failures, third parties, force majeure, degraded service, and claim procedures vary by agreement. Apply the actual contract; this tool provides transparent arithmetic, not legal interpretation.
Worked SLA and uptime examples
99.99% monthly and yearly downtime
2,592,000 × 0.0001 = 259.2 seconds, or 4 minutes 19.2 seconds per 30 days. For 365 days: 31,536,000 × 0.0001 = 3,153.6 seconds, or 52 minutes 33.6 seconds.
Actual uptime after a two-hour outage
In 30 days: (720 hours - 2 hours) ÷ 720 × 100 = 99.722222%. A 99.9% target would be missed because two hours exceeds its 43-minute 12-second allowance.
Required uptime for four hours downtime
(720 hours - 4 hours) ÷ 720 × 100 = 99.444444%. Rounded to four decimal places, the required target is 99.4444%.
Exhausted 99.9% error budget
Sixty minutes in a 30-day budget of 43 minutes 12 seconds is 60 ÷ 43.2 = 138.89% consumed, exceeding the allowance by 16 minutes 48 seconds. Over a one-day lookback, the failure-rate burn rate is (60 ÷ 1,440) ÷ 0.001 = 41.67×.
SLA uptime calculator FAQs
How is allowed downtime calculated?
Multiply the period duration by the unavailable fraction: allowed downtime = period × (1 - target / 100). A 99.9% target has a 0.1% unavailable fraction.
How much downtime does 99.9% allow per month and year?
At 99.9%, an exact 30-day month allows 43 minutes 12 seconds. A 365-day year allows 8 hours 45 minutes 36 seconds. An average calendar month of 365.2425 days divided by 12 allows about 43 minutes 49.7 seconds.
What is the difference between 99.9% and 99.99% uptime?
99.99% permits one tenth as much downtime as 99.9%. Over 30 days, the allowance falls from 43 minutes 12 seconds to 4 minutes 19.2 seconds, a reduction of 38 minutes 52.8 seconds.
What do three, four, and five nines mean?
Three nines means 99.9%, four nines means 99.99%, and five nines means 99.999%. Each extra nine cuts the unavailable fraction, and therefore allowed downtime, by a factor of ten.
How do I calculate uptime from downtime?
Subtract downtime from the total period, divide by the total period, then multiply by 100. Four hours of downtime in an exact 30-day period corresponds to 99.4444% uptime.
Does planned maintenance count as downtime?
It depends on the SLA or SLO policy. Some agreements exclude approved maintenance windows; others count every unavailable minute. Apply the inclusions and exclusions in the governing agreement.
How do rolling and calendar windows differ?
A calendar window resets on fixed dates, while a rolling window continuously evaluates the immediately preceding duration. The same incident can therefore affect the two windows differently.
Do partial outages count?
They may. Time-only calculations treat a service as up or down, while request-based SLIs can represent partial impact through failed eligible events. Use the SLI and weighting rules in the service definition.
What does an SLA breach usually trigger?
Possible outcomes include service credits, remediation duties, review, or termination rights, but there is no universal consequence. Check the agreement's measurement, exclusion, claim, and remedy clauses.
