Uptime SLA Calculator
Compute allowed downtime per period for 99%–99.999% SLAs.
What does an SLA like “99.9% availability” actually allow in downtime? Enter a target availability (%) and this calculator converts it into the maximum allowed downtime per day, week, month, quarter and year.
Use it to design SLAs, compare cloud/hosting guarantees, or judge whether an outage breached a contract. To also gauge the infrastructure cost as traffic grows, pair it with the bandwidth cost calculator.
| Day | 1m 26s |
|---|---|
| Week | 10m 5s |
| Month (30d) | 43m 12s |
| Quarter (90d) | 2h 9m 36s |
| Year (365d) | 8h 45m 36s |
The meaning of "nines"
Availability is often counted in "nines." Each extra nine cuts allowed downtime by roughly 10×.
- 99%: ~3.65 days/year
- 99.9%: ~8.76 hours/year
- 99.99%: ~52.6 minutes/year
- 99.999%: ~5.26 minutes/year
Allowed-downtime reference table
Per-year figures are hard to feel. Because SLA breaches are usually judged per month (commonly a fixed 30 days), here are the headline availability tiers laid out on the same basis this calculator uses (month = 30 days, quarter = 90 days, year = 365 days).
| Availability | Day | Month (30d) | Year (365d) |
|---|---|---|---|
90% (one nine) | 2h 24m | 3 days | 36.5 days |
95% | 1h 12m | 1.5 days | 18.25 days |
99% (two nines) | 14m 24s | 7h 12m | 3.65 days |
99.9% (three nines) | 1m 26s | 43m 12s | 8h 46m |
99.95% | 43s | 21m 36s | 4h 23m |
99.99% (four nines) | 8.6s | 4m 19s | 52m 36s |
99.999% (five nines) | 0.86s | 26s | 5m 16s |
99.95% and 99.99% are included because they are the tiers most cloud providers publish for standard SLAs (e.g. virtual machines and managed databases).
Worked example: 99.95%
Enter 99.95 and the "downtime fraction" is (100 − 99.95) ÷ 100 = 0.0005, i.e. 0.05%. Multiply that by the total minutes in each window.
- Month (30d) = 43,200 min × 0.0005 = 21.6 min → 21m 36s
- Year (365d) = 525,600 min × 0.0005 = 262.8 min → 4h 22m 48s
So a service promising 99.95% that is down for more than ~22 minutes in a single month has breached that month's SLA — typically triggering a service credit worth a set percentage of the bill.
Common pitfall
The most frequent mistake is reading downtime only on a yearly basis. Seeing "99.9% = 8.76 hours/year" makes a day of outage feel acceptable, but most SLAs reconcile per month, where the budget is just ~43 minutes — and a single long incident can burn the entire month's allowance at once. A second trap is averaging nines into a "99.9% on average" claim: availability is judged separately each billing period, not averaged, and serial dependencies multiply it down rather than up.