# What is Uptime?

> The share of time a service is available and working, usually shown as a percentage.

Canonical: https://www.decimal.app/glossary/uptime · Last reviewed: 2026-09-23

Uptime measures how much of a period a service was operational. It's often expressed in nines: 99.9% allows about 43 minutes of downtime a month, 99.99% about four.

## Why it matters

Uptime is a headline reliability promise and a frequent SLA term. But a service can be 'up' while failing for one customer, which is why support tickets often catch problems uptime checks miss.

## Best practices

1. Measure from the outside. Synthetic checks see what customers see.
2. Define 'up' carefully. Include degraded performance, not just total outages.
3. Reconcile with tickets. If customers report failures during 'up' periods, the check is too shallow.

## How Decimal helps

Decimal investigates the customer-specific failures that slip past uptime checks and traces them to the service or config behind them.

## Related terms

- [Service Level Objective (SLO)](https://www.decimal.app/glossary/slo): An internal reliability target, like 99.9% of requests succeeding.
- [Service Level Agreement (SLA)](https://www.decimal.app/glossary/sla): A contractual commitment on response or resolution times.
- [Incident](https://www.decimal.app/glossary/incident): An unplanned disruption or degradation of a service that needs an urgent response.
- [Status Page](https://www.decimal.app/glossary/status-page): A public page reporting current service health and active incidents.

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