# Uptime SLA Calculator

- **URL:** https://codeasystem.com/calculators/developer/uptime-sla-calculator/
- **Category:** developer
- **Description:** Translate an availability percentage into the exact downtime budget per day, 30-day month and year, humanized as clock time.
- **Primary output:** Allowed downtime per 30-day month: 43:12

## Inputs
- Availability SLO (name: `availability`, type: number, example: 99.9)

## Outputs
- Allowed downtime per 30-day month: 43:12
- Allowed per day: 01:26
- Allowed per year: 08:45:36
- Availability as error budget: 0.1%

## Formula / methodology
```
downtime = window × (1 − availability)
windows: 86,400 s/day · 2,592,000 s/30-day month · 31,536,000 s/year
```

Availability is the fraction of time a service must answer. Multiply each calendar window by (1 − availability) to get the allowed outage seconds, then format them as mm:ss or hh:mm:ss so budgets feel concrete in on-call reviews.

## Assumptions & limitations
- 30-day month = 2,592,000 seconds; year = 365 days.
- All partial outages count against the budget equally.
- Scheduled maintenance counts or not per your contract; this shows raw math.

## How to use
1. **Enter the promised availability**; Take it straight from your SLA contract or internal SLO, e.g. 99.9.
2. **Read the budgets**; Per-day, per-month and per-year figures show how little (or much) failure time the number buys.

## Example
A 99.9% SLO permits 86.4 seconds of downtime per day and exactly 43 minutes 12 seconds per 30-day month (2,592,000 × 0.001).

Result for these inputs:

```
Allowed downtime per 30-day month: 43:12
```

## About this calculator
### Nines escalate brutally

- 99% (“two nines”); 3.65 days/year
- 99.9%; 8.77 hours/year
- 99.99%; 52.6 minutes/year
- 99.999%; 5.26 minutes/year

### Budgets drive design

Each additional nine typically demands redundant everything: multi-zone deployments, automated failover, canary rollouts. Knowing that 99.9% allows only 43 minutes monthly reframes “minor incidents”; one forgotten alert can spend the month’s entire budget.

## FAQs
### Why use a 30-day month?

It is the industry convention (2,592,000 s) making months comparable; real months vary 28–31 days, so contracts specify which they mean.

### Does planned maintenance count?

Contracts differ. This tool shows raw unavailability budgets; subtract agreed maintenance windows from the allowance yourself.

### How do I measure actual availability?

Aggregate probe results over the window: successful requests (or seconds up) divided by total. Compare against this budget weekly.

## Related calculators
- [Error Budget Calculator](https://codeasystem.com/calculators/developer/error-budget-calculator/)
- [SRE Burn Rate Calculator](https://codeasystem.com/calculators/developer/sre-burn-rate-calculator/)
- [Rate Limit Planner](https://codeasystem.com/calculators/developer/rate-limit-calculator/)

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Last updated: 2026-08-23 · Version: 1.0.0 · [HTML version](https://codeasystem.com/calculators/developer/uptime-sla-calculator/)