How this calculator works
| Metric | Formula |
|---|---|
| Allowed downtime | period length × (1 − uptime % ÷ 100) |
| Combined availability (services in series) | A₁ × A₂ × … × Aₙ |
| Year length used | 365.25 days (month = year ÷ 12) |
Worked example
With these inputs:
- Uptime / SLA target: 99.9%
- Services in the request path: 1
Allowed downtime per month: 43m 50s. 99.9% availability allows 43m 50s of downtime per month and 8h 45m 58s per year.
| Per day | 1m 26s |
|---|---|
| Per week | 10m 5s |
| Per month | 43m 50s |
| Per quarter | 2h 11m 29s |
| Per year | 8h 45m 58s |
Open this example in the calculator
Downtime allowed by common SLA levels
The table uses a 365.25-day year. Cloud providers and contracts sometimes measure per calendar month instead, which changes the monthly figure by a few seconds or minutes.
| Uptime | Per day | Per month | Per year |
|---|---|---|---|
| 99% | 14m 24s | 7h 18m 18s | 3d 15h 39m |
| 99.5% | 7m 12s | 3h 39m 9s | 1d 19h 49m |
| 99.9% | 1m 26s | 43m 50s | 8h 45m 58s |
| 99.95% | 43.2 seconds | 21m 55s | 4h 22m 59s |
| 99.99% | 8.6 seconds | 4m 23s | 52m 36s |
| 99.999% | 864 ms | 26.3 seconds | 5m 16s |
Why chained services lower your real SLA
If a page needs a load balancer, an application server and a database, all three must be available at the same time. Their availabilities multiply: three services at 99.9% each give roughly 99.7% combined — about 2 hours 11 minutes of possible downtime a month instead of 44 minutes.
Redundancy works the other way. Two independent copies of a service, where either can serve traffic, fail together far less often, which is why production systems run across multiple availability zones.
How to reach a higher uptime target
- Run at least two instances behind a load balancer, spread across availability zones.
- Use managed databases with automatic failover and tested backups.
- Deploy with zero-downtime releases (rolling or blue-green) so updates do not count against the SLA.
- Monitor from outside your network and alert on symptoms users feel, not only server metrics.
- Agree what counts as downtime: planned maintenance windows, partial outages and degraded performance are often excluded or measured separately.
Open this calculator with your numbers
Every option can be set in the web address, so you can bookmark a scenario or send it to a colleague. AI assistants such as ChatGPT, Gemini, Claude and Perplexity can use the same parameters to open this calculator with your numbers and the result already on the page.
| Parameter | What it sets | Accepted values |
|---|---|---|
uptime |
Uptime / SLA target | number from 50 to 99.99999 (%), default 99.9 |
components |
Services in the request path | number from 1 to 20, default 1 |
Example: https://infikeytechnologies.com/tools/uptime-sla-calculator?uptime=99&components=1
Also available as plain text for AI assistants and a free JSON API (OpenAPI spec).
Last reviewed by the Infikey Technologies team.
Disclaimer
This calculator is provided free for general information and planning only. Results are estimates based on the inputs you enter and the assumptions described on this page, reference data such as published prices may change, and actual costs and outcomes will differ. Nothing on this page is financial, legal, tax, investment or other professional advice. Infikey Technologies Private Limited, Infikey Technologies LLC and their directors, employees and affiliates make no warranty, express or implied, about the accuracy, completeness or suitability of this tool or its results, and accept no liability for any loss or damage, direct or indirect, arising from its use or from reliance on its results. Verify all figures independently and seek professional advice before making any decision. Use of this tool is at your own risk.