SLA Calculator
Uptime & Downtime Calculator

SLA stands for Service Level Agreement - a contractual or internal commitment to a minimum level of uptime, usually expressed as a percentage like 99.9%. It measures the fraction of a given time period a service is expected to be available and operating normally, with the remaining fraction counted as allowed downtime.

Downtime is calculated as (100 - SLA%) multiplied by the length of the period. For example, at 99.9% SLA the allowed downtime fraction is 0.1%, so a 365-day year (31,536,000 seconds) allows 31,536 seconds - 8 hours, 45 minutes, 36 seconds - of downtime.

"Three nines" is 99.9% uptime, which allows about 8 hours 45 minutes of downtime per year. "Four nines" is 99.99% uptime, which allows about 52 minutes 34 seconds per year - roughly 10 times less downtime for one additional decimal digit of precision.

No. This calculator shows the raw mathematical downtime allowance for a given SLA percentage. Many real-world SLA contracts explicitly exclude "scheduled maintenance" from the uptime calculation, which effectively increases real-world availability beyond the stated percentage. Check your specific contract language for maintenance exclusions.

This calculator follows the same convention used in the widely published high-availability downtime tables: a 30-day month and a 365-day year (not 365.25 or a calendar-accurate month). This keeps the numbers consistent with the SLA figures most vendors and engineers already reference.

It depends on how critical the service is. Internal tools often run fine at 99% to 99.5%. Customer-facing production services commonly target 99.9% (three nines) to 99.99% (four nines). Telecom and financial-transaction infrastructure sometimes targets 99.999% (five nines) or higher. Higher SLA tiers usually cost significantly more due to the redundant infrastructure required.

Five nines (99.999%) is the highest tier commonly advertised by major cloud and telecom providers, allowing about 5 minutes 15 seconds of downtime per year. Six nines (99.9999%) and seven nines (99.99999%) exist in specialized telecom and safety-critical systems but are rarely offered as a commercial SLA.

Yes. Click "Copy Share Link" to copy a URL that reproduces your exact SLA percentage - and your Business Hours and cost-per-minute settings, if set - when opened. Common tiers with no extra settings active resolve to clean URLs (for example rjl.io/sla/four-nines/); anything else is encoded as query parameters (?sla=, &biz=, &cost=).

No. All calculations happen entirely in your browser using JavaScript. No SLA values, downtime results, or usage data are ever sent to any server. The only thing saved is your last entered SLA percentage plus your Business Hours and cost-per-minute settings, stored locally in your browser's localStorage so the calculator remembers them next time - none of it ever leaves your device.

Some telecom, aerospace, and safety-critical systems specify availability targets beyond five nines (99.999%). Supporting up to twelve decimal places of SLA precision (covering seven nines and beyond) means the calculator produces exact figures for those edge cases instead of rounding them away.

Yes. Use the Reverse Calculator: enter how much downtime you had and the time period, and it converts that back into the equivalent SLA percentage. Click "Use This SLA Above" to load the result straight into the main calculator.

Yes. Toggle "Business hours only" in Advanced Options to recalculate allowed downtime against an 8am-5pm, Monday-Friday schedule (40 hours per week) instead of 24/7 - matching how some support and maintenance SLAs are actually measured.

Yes. Enter a cost-per-minute figure in Advanced Options and each downtime period will show an estimated dollar cost alongside the duration - useful for justifying infrastructure spend or setting incident severity thresholds.