Uptime & SLA Calculator
Convert downtime into availability, find the allowed downtime for any SLA tier, and see exactly what 99.9%, 99.99%, and 99.999% mean per day, week, month, and year.
Enter your downtime
Resulting Availability
99.8973305955%
45m of downtime out of 30d 10h 30m total
AcceptableSLA Tier Reference
Allowed downtime for each common SLA tier.
| SLA Tier | Name | Allowed Downtime |
|---|---|---|
| 99% | Two nines | 7h 18m 18s |
| 99.9% | Three nines | 43m 50s |
| 99.95% | Three and a half nines | 21m 55s |
| 99.99% | Four nines | 4m 23s |
| 99.999% | Five nines | 26s |
| 99.9999% | Six nines | 3s |
Period basis: 30d 10h 30m (month).
Uptime, SLAs, and Availability: A Practical Guide
An uptime calculator converts between two ways of talking about reliability: a percentage like 99.9% and a concrete amount of downtime like 43 minutes per month. Percentages are abstract; minutes are real. This tool bridges that gap so you can set meaningful targets, evaluate provider SLAs, and quantify incidents.
The Math Behind Uptime
Uptime percentage is defined as the time a service was available divided by total elapsed time:
where T is the total period (a month, a year) and D is the downtime within it. A 30-day month is 43,200 minutes; 43 minutes of downtime gives (43157 / 43200) × 100 ≈ 99.9%.
What the "Nines" Really Mean
Each additional nine cuts allowed downtime by roughly 90%:
- 99%Two nines. ≈ 7.2 hours of downtime per month. Acceptable for low-stakes sites.
- 99.9%Three nines. ≈ 43 minutes per month. The standard baseline for most hosting and SaaS SLAs.
- 99.99%Four nines. ≈ 4.3 minutes per month. Requires redundant infrastructure and automated failover.
- 99.999%Five nines. ≈ 26 seconds per month. The telecom and finance standard; extremely expensive to achieve.
How to Use the Uptime Calculator
Switch between two modes at the top. Downtime → Uptime answers "we were down for 2 hours last month, what's our availability?" SLA → Allowed Downtimeanswers "our contract guarantees 99.95%, how much downtime can we have this year?"
Choose any time unit (minutes, hours, days) for downtime and any period (day, week, month, year, or a custom number of days) for the basis. The SLA tier reference table below the calculator shows allowed downtime for every common tier so you can compare targets at a glance.
Reading an SLA Contract
A Service Level Agreement (SLA) is a provider's commitment to uptime, usually expressed as a monthly or annual percentage. But the percentage alone is not the whole story — read the fine print for:
- Measurement window. Monthly windows hide big outages better than daily or annual ones.
- Exclusions. Scheduled maintenance, force majeure, and upstream provider failures are often excluded from the calculation.
- Remedy. SLA breaches usually yield service credits, not cash refunds — and often capped at a fraction of your monthly bill.
Frequently Asked Questions
Uptime is the percentage of time a service is operational and accessible. It is calculated as (total time minus downtime) divided by total time, multiplied by 100. For example, 43 minutes of downtime in a 30-day month equals roughly 99.9% uptime. The complement, downtime, is any period the service is unavailable or unresponsive.
Each nine in an SLA dramatically reduces allowed downtime. 99% allows about 7.2 hours per month, 99.9% (three nines) allows about 43.2 minutes, 99.99% (four nines) allows about 4.32 minutes, and 99.999% (five nines) allows about 26 seconds. Use the calculator above to convert any SLA percentage into exact downtime for any period.
For most websites, 99.9% (about 43 minutes of downtime per month) is considered a solid baseline and is the standard promised by many cloud and hosting providers. Mission-critical applications often target 99.99% or 99.999%, but each additional nine costs disproportionately more in infrastructure, redundancy, and engineering effort.
Availability equals (period length minus downtime) divided by period length. The calculator lets you enter downtime in any unit (minutes, hours, or days) and select the period (a day, week, month, or year) to get the resulting uptime percentage instantly.
No. The uptime calculator runs entirely in your browser. No uptime figures, SLA inputs, or calculation results are sent to a server or stored anywhere. You can use it for confidential business planning without any data leaving your device.