# Availability Percentage Calculator

> Measure availability from actual downtime over a period, or from MTBF and MTTR, and see the number of nines and the downtime that rate implies per year.

Category: IT, networking & security · Applies to: Worldwide · Last updated: 2026-10-29
Interactive calculator: https://calculators.geekmidst.com/calculators/availability-percentage-calculator

Availability is the share of time a service was usable: uptime divided by the time measured. Enter observed downtime, or mean time between failures and mean time to recover, to get the percentage and its “nines”.

Also called: Uptime percentage calculator.

## Inputs
- Calculate from (options: Measured downtime, MTBF and MTTR; default downtime)
- Measurement period (unit days; default 30)
- Unplanned downtime (unit min; default 43.2)
- Excluded planned maintenance (unit min; default ; optional)
- Mean time between failures (unit h; default 999)
- Mean time to recover (unit h; default 1)

## Results
- Availability
- Number of nines
- Unavailability
- Downtime per year at this rate
- Downtime per 30-day month
- Downtime per week

## Formula

```
Availability = (Measured time − Downtime) ÷ Measured time, where Measured time = Period − Excluded maintenance;  or Availability = MTBF ÷ (MTBF + MTTR);  Nines = −log₁₀(1 − Availability)
```

Where:
- Downtime: unplanned time the service was unusable
- MTBF: mean time between failures
- MTTR: mean time to recover
- Year: 365.25 days (525,960 minutes)

## Worked example
1. Measured time = 30 × 1,440 = 43,200 min.
2. Availability = (43,200 − 43.2) ÷ 43,200 = 99.9%.
3. At that rate a year has 0.1% × 525,960 = 525.96 min (about 8.77 h) of downtime.

**Result:** 43.2 minutes of downtime in 30 days is 99.9% availability, or three nines.

## What the result means

Compare the result with your SLA or SLO. Each extra nine cuts allowed downtime by a factor of ten, which usually needs a step change in architecture, not just faster fixes.

## Assumptions and limits
- Downtime is total: partial outages count fully unless you weight them yourself.
- The MTBF/MTTR form is a steady-state average; short periods with few incidents can differ a lot from it.

## Questions

### How is this different from an SLA downtime calculator?

An SLA downtime calculator starts from a target such as 99.9% and tells you how much downtime it allows. This page starts from what actually happened and gives the availability achieved.

### Does planned maintenance count as downtime?

It depends on your SLA. Many exclude announced maintenance; enter it in the excluded field to remove it from the measured period.

## Related calculators
- [Mean Time to Recover (MTTR) Calculator](https://calculators.geekmidst.com/calculators/incident-mean-time-to-recover-calculator)
- [Percentage Calculator](https://calculators.geekmidst.com/calculators/percentage-calculator)
- [Time Duration Calculator](https://calculators.geekmidst.com/calculators/time-duration-calculator)
- [Uptime SLA Downtime Calculator](https://calculators.geekmidst.com/calculators/website-uptime-sla-downtime-calculator)

Source: GM¹X CalcVerse — https://calculators.geekmidst.com/calculators/availability-percentage-calculator