% Calculate Allowed Downtime
Downtime / Day
1m 26s
Downtime / Week
10m 5s
Downtime / Month
43m 50s
Downtime / Year
8h 45m
At $100/hr, your maximum annual downtime costs up to
$876
★ The Nines of Availability
Industry-standard SLA tiers and their allowed downtime. The difference between "three nines" and "five nines" is the difference between a few hours and a few minutes of annual downtime.
| Name | Uptime % | Downtime/Year | Downtime/Month | Downtime/Day |
|---|---|---|---|---|
| One Nine | 90% | 36d 12h | 3d 0h | 2h 24m |
| Two Nines | 99% | 3d 15h 36m | 7h 18m | 14m 24s |
| Three Nines | 99.9% | 8h 45m 36s | 43m 50s | 1m 26s |
| Four Nines | 99.99% | 52m 34s | 4m 23s | 8.6s |
| Five Nines | 99.999% | 5m 15s | 26.3s | 0.86s |
| Six Nines | 99.9999% | 31.5s | 2.6s | 0.086s |
⇄ Reverse Calculator — Downtime to Uptime
Enter your actual downtime to calculate your real uptime percentage.
Your Actual Uptime
99.931%
Between Three and Four Nines
SLA Tier
Three Nines (99.9%)
0.031% margin above SLA
Don't find out about downtime from your users
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Start monitoring free →Frequently Asked Questions
What does 99.9% uptime actually mean?
99.9% uptime (often called "three nines") means your service can be down for a maximum of 8 hours, 45 minutes, and 36 seconds per year. That's about 43 minutes and 50 seconds per month, or 1 minute and 26 seconds per day. Most SaaS companies target this level as it balances reliability with engineering cost.
What's the difference between 99.9% and 99.99% uptime?
The difference is massive in practice: 99.9% allows about 8 hours 46 minutes of annual downtime, while 99.99% allows only 52 minutes and 34 seconds per year. Moving from three nines to four nines typically requires redundant infrastructure, automatic failover, and sophisticated monitoring — which is why the engineering cost increases dramatically with each additional nine.
How do I calculate SLA uptime percentage?
Uptime percentage = ((Total time - Downtime) / Total time) × 100. For example, if your service was down for 4 hours in a 30-day month (720 hours): ((720 - 4) / 720) × 100 = 99.44%. This calculator does this math automatically — enter your downtime in the reverse calculator above to see your actual uptime percentage.
What SLA level should I target?
It depends on your use case. Most B2B SaaS products target 99.9% (three nines). Payment processors and financial services often aim for 99.99% (four nines). Critical infrastructure like DNS providers target 99.999% (five nines). Each additional nine roughly 10x the engineering effort and cost. Start with 99.9% and invest in higher availability only when your customers' needs justify the cost.
Does scheduled maintenance count as downtime?
It depends on your SLA agreement. Some SLAs exclude planned maintenance windows from downtime calculations. Others include all downtime regardless of cause. Best practice is to be explicit in your SLA about what counts: include definitions for "scheduled maintenance," "emergency maintenance," and "unplanned outage" separately. Most modern services aim for zero-downtime deployments to avoid this question entirely.
How do I monitor if I'm meeting my SLA?
You need continuous monitoring of all critical endpoints and background processes. Use an external monitoring service (like CronPing for cron jobs and scheduled tasks) that checks your services from outside your infrastructure. Track uptime metrics over 30-day rolling windows, set alerts for anomalies, and maintain a public status page so customers can see your track record. The key is catching issues before your customers do.