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SLA Uptime Calculator

Calculate downtime from SLA uptime

How to Use

  1. Select the calculation mode (Uptime → Downtime or Downtime → Uptime)
  2. Uptime mode: Enter the uptime (%) or click a preset button (99.9%, etc.)
  3. The allowable downtime per year, month, week, or day is automatically calculated
  4. Reverse calculation mode: Enter the downtime duration and reference period to calculate uptime
  5. Click the "Copy" button to copy the calculation result to the clipboard

Use Cases

  • Checking downtime when considering SLA (Service Level Agreement) for cloud services
  • Determining which uptime target should be set during system design
  • Calculating SLA achievement rate from actual downtime in incident reports
  • Setting availability targets for multi-region configurations or failover design

Frequently Asked Questions

What is the difference between 99.9% and 99.99%? ▼

99.9% (three nines) allows approximately 43 minutes of downtime per month. 99.99% (four nines) allows approximately 4.3 minutes per month. When you add one more digit, downtime becomes approximately one-tenth, and the required redundancy and cost increase significantly.

Why is the calculation using 1 year = 365.25 days? ▼

We use 365.25 days as an average value accounting for leap years. This is a standard value widely used in SLA calculations. Similarly, 1 month = 30.4375 days is the value of 365.25 ÷ 12.

Is the data I enter sent to a server? ▼

No, all calculations are completed in the browser. Input data is never sent externally.

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