# Uptime nines converter

Convert an availability percentage into allowed downtime per day, week, month and year, or a month of downtime into availability.

## How it works

Each extra nine cuts allowed downtime by ten times: 99.9% allows about 43 minutes a month, 99.99% about 4.

```
downtime = (1 − availability) × period
```

## Questions

### How many nines do I need?

Match what users notice and what you can afford. Each extra nine usually costs far more than the last.

### Does planned maintenance count?

It depends on your definition. Most SLOs count anything users see as down.

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