# Availability Calculator

> Work out availability from your own MTBF and MTTR.

Page: https://freecalculator.tech/tools/availability-calculator
Last reviewed: 2026-09-16

## Formula

A = MTBF / (MTBF + MTTR)

- A = MTBF / (MTBF + MTTR).
- Inputs used: Mean time between failures (MTBF), Mean time to repair (MTTR).
- Edge handling: Mean time between failures (MTBF) is required.; Mean time between failures (MTBF) cannot be negative.; Mean time between failures (MTBF) must be no more than 1000000000000.; Mean time to repair (MTTR) is required.; Mean time to repair (MTTR) cannot be negative..

## Inputs

- Mean time between failures (MTBF)
- Mean time to repair (MTTR)

## Worked example: 720 hours between failures, 2.5 hours to repair

Availability from your own reliability data. No target availability is implied.
1. Start with Mean time between failures (MTBF): 720, Mean time to repair (MTTR): 2.5.
2. Apply the method: A = MTBF / (MTBF + MTTR).
3. Availability from your own reliability data. No target availability is implied.

## Common questions

### Where does this formula come from?

Section 8.1.2.4 — mean time between failures is operating time divided by the number of failures; mean time to repair is total repair time divided by the number of repairs; inherent availability is MTBF / (MTBF + MTTR). See the source link on this page.

### What kind of calculation is this?

The share of a failure-and-repair cycle during which the service is operating. Check the formula, example, and limitations on this page before using the result for a real professional & industry decision.

### What are its limits?

Arithmetic over the figures entered — it cannot tell whether the underlying monitoring, incident records or change records are complete. A mean over a short period, or over few events, is a weak description of behaviour. Inherent availability excludes delays outside repair itself, so it is usually higher than availability as the user experiences it.

### How do I use the Availability Calculator?

Enter the required values for Mean time between failures (MTBF), Mean time to repair (MTTR). The calculator applies the formula on this page and shows the main result with any supporting breakdown so you can check the arithmetic.

### What formula does the Availability Calculator use?

A = MTBF / (MTBF + MTTR) The visible formula section above lists the calculation path and the edge cases the page handles, so the result can be checked without relying on the form alone. Check the formula, example, and limitations on this page before using the result for a real professional & industry decision.

### Can the Availability Calculator be used for exact decisions?

Use it as a calculation aid, not as a substitute for checking the underlying rule, contract, policy, or professional advice that applies to your situation. When a result depends on local rules, personal details, prices, or dates, enter those values yourself and confirm them before acting.

## Limitations and assumptions

- Inputs outside the supported range are rejected rather than forced into a result.
- The result depends on the values you enter for this availability calculator; it does not supply missing rates, rules, prices, dates, or assumptions for you.

## Sources

- National Institute of Standards and Technology — https://www.itl.nist.gov/div898/handbook/apr/section1/apr124.htm

## Cite this page

- APA: Free Calculator. (2026, September 16). Availability Calculator. https://freecalculator.tech/tools/availability-calculator
- MLA: "Availability Calculator." Free Calculator, 16 Sept. 2026, https://freecalculator.tech/tools/availability-calculator.
- Link: Availability Calculator — Free Calculator, https://freecalculator.tech/tools/availability-calculator