SLA Uptime Calculator

Why use an SLA uptime calculator?

Service Level Agreements (SLAs) define your availability commitment. An SLA uptime calculator converts percentages like 99%, 99.9%, or 99.99% into real downtime in minutes and hours, so you can clearly understand what your uptime promise actually means.

• See exactly how much downtime is allowed per year, month, week, or day to plan maintenance windows and incident response more effectively.
• Compare uptime levels like 99.9% vs 99.99% vs 99.999% and understand the real-world difference in minutes, not just percentages.
• Estimate the financial impact of downtime with optional revenue-based calculations to prioritise reliability and infrastructure investment.
• Communicate SLA commitments clearly to customers, stakeholders, and internal teams using concrete time values instead of abstract availability percentages.

An SLA uptime calculator transforms availability percentages into measurable downtime so you know exactly what you're promising — and what's at risk.

About this tool

Our free uptime calculator (also known as an SLA calculator, downtime calculator, availability calculator, system uptime calculator, or uptime percentage calculator) converts any uptime percentage into the actual allowed downtime per year, month, week, and day. Enter a value like 99.9% or 99.99% and instantly see what that promise really means in minutes and hours. No account or signup required.

How to calculate uptime and downtime

The uptime calculation formula is straightforward. Downtime is the inverse of uptime, expressed as a fraction of total time in the measurement period.

Uptime % = (Total time − Downtime) / Total time × 100
Allowed downtime = Total time × (1 − Uptime %/100)

For example, a 99.9% uptime SLA over a year (8,760 hours) allows 8,760 × (1 − 0.999) = 8.76 hours of downtime, which works out to about 43 minutes per month. Bumping to 99.99% drops your allowed downtime by an order of magnitude, to roughly 52 minutes per year.

How it works

1. You enter an uptime percentage (any value between 1% and 100%, including fractional values like 99.95%).
2. The calculator runs the downtime formula across four standard periods: daily, weekly, monthly (30 days), and yearly (365 days).
3. Toggle between Downtime and Uptime views to see either how much outage is allowed or how much availability is required.
4. Optionally enter your monthly or yearly revenue and the calculator estimates the financial impact of every minute, hour, day, week, month, or year of downtime.

Related reading

For context on what these uptime percentages actually mean for different types of businesses, read our guide on what counts as a good uptime percentage (covers AWS, Azure, and Google Cloud SLAs). If you want to start tracking your own actual uptime against an SLA, see our guides on how to monitor website uptime and detecting server downtime.

Also useful for: uptime SLA calculation, system availability calculation, downtime percentage calculation, calculating allowed downtime from an SLA, comparing 99% vs 99.9% vs 99.99% vs 99.999% uptime, and estimating the revenue cost of outages.