System Uptime Calculator

Convert outages into trusted availability metrics fast. Model SLA targets with downtime budgets per period. Download clean reports for reviews, compliance, and planning teams.

Inputs

Pick the data you have.
Used for totals, and for MTBF report scaling.
Includes incident time within the window.
Local time, inclusive.
Local time, exclusive.
Lines outside the window are clipped. Invalid lines are ignored.
Higher MTBF usually improves availability.
Lower MTTR reduces expected downtime.
%
Used to compute allowed downtime budget.
Month/year variants help match your SLA convention.
Subtracts planned time from the denominator.
Tip: For interval mode, copy incident start/end times from monitoring logs.

Example data table

Sample monthly reporting view for a single service.

Period Total window Downtime Availability Notes
2026-01 30d 00h 00m 00s 00h 32m 10s 99.9256% Two brief incidents.
2026-02 28d 00h 00m 00s 01h 12m 00s 99.8214% One regional outage.
2026-03 31d 00h 00m 00s 00h 05m 30s 99.9877% Patch window excluded.

Formula used

If you exclude maintenance, the calculator subtracts that time from the denominator, matching common reporting policies for planned windows.

How to use this calculator

  1. Choose the method that matches your data source.
  2. Enter your reporting window length for the period you report on.
  3. Provide downtime as a single total, or paste incident intervals.
  4. Optionally exclude planned maintenance to reflect your policy.
  5. Set a target availability and period to see downtime budget.
  6. Press Calculate to view results above the form.
  7. Download CSV for spreadsheets, or PDF for sharing.

FAQs

1) What is the difference between uptime and availability?

Uptime is the time a service is running. Availability is uptime divided by the measured window, expressed as a percentage for easy comparison.

2) How do “nines” relate to availability?

“Nines” summarize how close availability is to 100%. For example, 99.9% is roughly three nines. It is a shorthand, not a full reliability analysis.

3) Should I exclude planned maintenance from uptime reporting?

It depends on your SLA and reporting rules. Some contracts exclude scheduled maintenance, while others count all time. This calculator supports either approach.

4) How do I enter incident intervals correctly?

Use one line per incident in the format start,end using the same datetime format as the inputs. Intervals outside your monitoring window are clipped automatically.

5) What does the downtime budget tell me?

The budget shows the maximum downtime allowed to meet your target availability over a chosen period. It helps plan error budgets and change management.

6) Can downtime exceed the reporting window?

No. If downtime is larger than the effective window, it is capped to the window to avoid impossible availability values.

7) When should I use the MTBF and MTTR method?

Use it when you model expected availability from reliability metrics rather than measured logs. It’s helpful early in design or for capacity planning assumptions.

8) Does this calculator handle overlapping incidents?

Interval mode sums intervals as entered. If you may have overlaps, merge them first to avoid double counting. Exporting CSV can help you validate entries.