SLA & Uptime Calculator: How Much Downtime Is Allowed?

An SLA calculator converts a service level agreement percentage (like 99.9%) into the exact amount of downtime that percentage allows per day, week, month, and year. Use it when negotiating SLAs with vendors, setting internal availability targets, or checking whether a provider stayed within their commitment after an outage.

The formula is: Allowed downtime = Period × (1 − SLA / 100). For a 99.9% SLA over a 30.44-day month, that's 2,629,746 seconds × 0.001 = 2,630 seconds, or about 43 minutes 50 seconds. This calculator uses 365.2425 days/year and 30.4369 days/month for precision.

99.9% uptime (three nines) allows 1 minute 26 seconds of downtime per day, 10 minutes 5 seconds per week, 43 minutes 50 seconds per month, and 8 hours 46 minutes per year. Most SaaS products target this level as the baseline for production services.

99.9% allows about 8 hours 46 minutes of downtime per year, while 99.99% (four nines) allows only 52 minutes 34 seconds. Each additional nine requires exponentially more investment in redundancy, failover automation, and operational discipline. Most web apps target 99.9%; critical financial infrastructure targets 99.99% or higher.

Uptime % = ((Total period − Downtime) / Total period) × 100. For example, 2 hours of downtime in a 30-day month: ((720 − 2) / 720) × 100 = 99.722%. Use the "Downtime → Uptime %" mode above to calculate this instantly.

It depends on the cost of downtime to your users. 99% is reasonable for internal tools, 99.9% for most SaaS products, 99.95%+ for services where outages directly cost customers money. Don't chase five nines as a vanity metric — the infrastructure cost grows exponentially while the user-perceptible difference shrinks.