Calculator Inputs
This calculator uses a responsive input grid: three columns on large screens, two on smaller screens, and one on mobile devices.
Example Data Table
Use these sample rows to understand how service availability assessments can be documented for different services and reporting windows.
| Service | Period | Target % | Eligible Minutes | Effective Downtime | Time Availability | Status |
|---|---|---|---|---|---|---|
| Checkout API | Monthly | 99.95% | 43,080 | 32.00 min | 99.9257% | Below target |
| Auth Gateway | Monthly | 99.90% | 43,200 | 18.50 min | 99.9572% | Within target |
| Media Storage | Quarterly | 99.50% | 129,600 | 410.00 min | 99.6836% | Within target |
Formula Used
1) Eligible Service Window
Eligible Service Window = Total Period Minutes − Excluded Planned Maintenance Minutes
2) Effective Downtime
Effective Downtime = Manual Downtime + Sum of Incident Durations + (Degraded Minutes × Impact Weight)
3) Time-Based Availability
Time-Based Availability (%) = ((Eligible Minutes − Effective Downtime) ÷ Eligible Minutes) × 100
4) Request Availability
Request Availability (%) = ((Total Requests − Failed Requests) ÷ Total Requests) × 100
5) Probe Availability
Probe Availability (%) = ((Total Checks − Failed Checks) ÷ Total Checks) × 100
6) Error Budget
Allowed Downtime = Eligible Minutes × (1 − Target Availability ÷ 100)
Remaining Error Budget = Allowed Downtime − Effective Downtime
7) MTBF and MTTR Availability Estimate
MTTR = Effective Downtime ÷ Incident Count
MTBF = Uptime Minutes ÷ Incident Count
Predicted Availability (%) = (MTBF ÷ (MTBF + MTTR)) × 100
How to Use This Calculator
- Enter a service name, service tier, and reporting period.
- Set the target availability percentage for the SLA or SLO.
- Enter scheduled maintenance minutes and decide whether to exclude them from the SLA window.
- Add manual downtime and incident duration values in minutes.
- Enter degraded minutes and the impact percentage for partial outages.
- Add request totals and failed requests for request-based availability.
- Add probe totals and failed probes for monitoring-based availability.
- Submit the form to view results above the form, inspect the chart, then export the summary as CSV or PDF.
FAQs
1. What does service availability measure?
Service availability measures how much of the eligible service window remained usable. It compares available time or successful operations against the expected service window.
2. Why exclude scheduled maintenance?
Many service agreements remove approved maintenance from the SLA window. Excluding it avoids penalizing planned work that stakeholders already accepted in advance.
3. What is an error budget?
An error budget is the maximum downtime allowed before the target is missed. It helps teams balance reliability work and feature delivery.
4. Why track request availability separately?
A service can stay online while still failing requests. Request availability captures user-facing outcomes more directly than pure time-based uptime.
5. What are degraded minutes?
Degraded minutes represent partial outages where the service worked poorly rather than fully failing. Weighting them reflects business impact more realistically.
6. How should I enter incident durations?
Enter incident durations in minutes using spaces, commas, semicolons, or line breaks. The calculator sums them automatically for the effective downtime total.
7. What do MTBF and MTTR tell me?
MTBF estimates average operating time between incidents. MTTR estimates average recovery time per incident. Together they provide a reliability-based availability estimate.
8. Which availability value should decision makers prioritize?
Use time-based availability for SLA tracking, request availability for customer impact, and probe availability for monitoring quality. Reviewing all three gives stronger decisions.