Uptime / SLA Calculator

What SLA nines mean

Service level agreements usually promise a minimum availability over a window. 99.9% sounds high until you convert it to minutes. Over 30 days, three nines still allow 43 minutes of downtime. Four nines drop that to a little over four minutes. Five nines is about 26 seconds.

The formula is simple: downtime = period × (1 − availability). This tool uses 24-hour days so a 30-day month is 720 hours and a year is 8,760 hours. That matches how most engineering teams budget error budgets, even if a legal contract names a specific calendar month.

SLA calculator FAQ

How is allowed downtime calculated?

Allowed downtime = period × (1 − SLA). For 99.9% over 30 days that is 0.1% of 720 hours, or 43 minutes and 12 seconds. The calculator uses 24-hour days and a 30-day month unless you set a custom period.

What are “nines” of availability?

Nines describe how many 9s appear in the percentage. 99% is two nines, 99.9% is three nines, 99.99% is four nines, and 99.999% is five nines. Each extra nine cuts allowed downtime by about 10×.

Should I use 30 days or a calendar month?

A 30-day month is the usual planning figure (720 hours). A 365-day year is 8,760 hours. Use the custom period if your contract measures a specific window, such as a billing month with 31 days.

Does this include planned maintenance?

Only if you count that time as downtime. Some contracts exclude scheduled maintenance from SLA burn. Enter only the outage minutes that count against the commitment.

How does monitoring help you meet an SLA?

You cannot manage what you do not measure. Uptime checks from multiple regions show when a service is actually down, how long it lasted, and whether you are still inside the allowed budget. Crystade health checks and status pages are built for that.