Calculator inputs
Use a full calendar month or a custom service window. Partial degradation is converted into weighted downtime for more realistic SLA tracking.
Example data table
| Month | Mode | Planned maintenance | Unplanned outage | Degraded service | Measured window | Availability | Status |
|---|---|---|---|---|---|---|---|
| April 2026 | Full month, planned excluded | 120 minutes | 45 minutes | 90 minutes at 50% impact | 43,080 minutes | 99.7911% | Below a 99.9% target |
| May 2026 | Business window, 12h × 5d | 60 minutes | 20 minutes | 40 minutes at 25% impact | 15,780 minutes | 99.8101% | Within a 99.5% target |
Formula used
1. Service window minutes
Full month mode uses all calendar minutes in the month. Custom service window mode uses:
operational days × service hours per day × 60
2. Measured window minutes
service window minutes − planned maintenance minutes when maintenance is excluded. Otherwise, it equals the full service window.
3. Weighted degraded downtime
degraded minutes × (impact percent ÷ 100)
This converts partial service loss into equivalent downtime.
4. Effective downtime
unplanned outage minutes + weighted degraded downtime
5. Availability percentage
((measured window minutes − effective downtime) ÷ measured window minutes) × 100
6. Downtime budget
measured window minutes × (1 − target SLA)
Compare actual downtime against this budget to determine whether the target was achieved.
How to use this calculator
- Select the reporting month and year.
- Choose Full month for always-on services or Custom service window for limited support hours.
- Enter planned maintenance, unplanned outage, and degraded service minutes.
- Set the degradation impact percentage to reflect partial loss severity.
- Enter your monthly incident count and target SLA percentage.
- Tick the checkbox if planned maintenance should not reduce uptime performance.
- Submit the form to see availability, downtime budget, MTTR, MTBF, and the chart.
- Use the export buttons to download a CSV report or a PDF summary.
FAQs
1. What does monthly uptime measure?
Monthly uptime measures the percentage of time your application remained available during the chosen month. It can reflect either the full calendar or only your defined operating hours, depending on your measurement model.
2. Why include degraded service minutes?
Some incidents do not fully take a system offline but still hurt users. Weighted degraded minutes convert partial service loss into equivalent downtime, producing a more realistic availability figure for reliability reviews.
3. Should planned maintenance count against uptime?
That depends on your contract or internal policy. Many teams exclude approved maintenance windows from the measured service period, while others keep them inside the denominator for stricter reporting.
4. What is the difference between full month and custom service window?
Full month assumes continuous service, twenty-four hours a day. Custom service window calculates only the operating hours and service days you choose, which is useful for internal tools or limited support platforms.
5. What does downtime budget mean?
Downtime budget is the maximum outage time allowed before missing the target SLA. It helps engineering teams judge whether current reliability performance is acceptable or requires corrective action.
6. How are MTTR and MTBF used here?
Observed MTTR divides effective downtime by incident count. Observed MTBF divides achieved uptime by incident count. Together, they help you understand recovery speed and failure spacing during the month.
7. Can this calculator support SLA reviews?
Yes. It compares actual availability against a target SLA, shows the remaining or exceeded downtime budget, and summarizes weighted outages for easier monthly service review discussions.
8. Why might uptime be high but still miss the target?
Targets like 99.9% or 99.99% allow very little downtime. A few minutes of incidents can still exceed the allowed threshold, especially in shorter service windows or strict contractual environments.