# Allowed Downtime Calculator

> See how much downtime the availability target you set allows.

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

## Formula

Allowed downtime = Period × (1 − Target availability)

- Allowed downtime = Period × (1 − Target availability).
- Inputs used: Availability target you have set, Length of the period.
- Edge handling: Availability target you have set is required.; Availability target you have set cannot be negative.; Availability target you have set must be no more than 100.; Length of the period is required.; Length of the period cannot be negative..

## Inputs

- Availability target you have set
- Length of the period

## Worked example: A 99.9% target over 30 days

The target is the one you entered; the calculator does not recommend one.
1. Start with Availability target you have set: 99.9, Length of the period: 30.
2. Apply the method: Allowed downtime = Period × (1 − Target availability).
3. The target is the one you entered; the calculator does not recommend one.

## Common questions

### Where does this formula come from?

Implementing SLOs — a service level objective is the share of good events among valid events (or of available time in the period); the error budget is the remainder that the objective permits. See the source link on this page.

### What kind of calculation is this?

The unavailable time an availability target leaves in the period. 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. Allowed downtime is an arithmetic consequence of the target, not advice about how much downtime is acceptable.

### How do I use the Allowed Downtime Calculator?

Enter the required values for Availability target you have set, Length of the period. 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 Allowed Downtime Calculator use?

Allowed downtime = Period × (1 − Target availability) 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 Allowed Downtime 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 allowed downtime calculator; it does not supply missing rates, rules, prices, dates, or assumptions for you.

## Sources

- Google — https://sre.google/workbook/implementing-slos/

## Cite this page

- APA: Free Calculator. (2026, September 16). Allowed Downtime Calculator. https://freecalculator.tech/tools/allowed-downtime-calculator
- MLA: "Allowed Downtime Calculator." Free Calculator, 16 Sept. 2026, https://freecalculator.tech/tools/allowed-downtime-calculator.
- Link: Allowed Downtime Calculator — Free Calculator, https://freecalculator.tech/tools/allowed-downtime-calculator