Don't like ads? Go Ad-Free Today 

Uptime / SLA Calculator

DeveloperMathNetworking

ADVERTISEMENT · REMOVE?

INPUT

Auto Process

Downtime allowed for a given SLA %

Required SLA % for a target max downtime

Error budget remaining this period

SLA Percentage

Common Tier

SLA %

Use decimals, max 6 places (e.g. 99.999)

Target Max Downtime

Max Downtime

Per Period

Elapsed Downtime So Far

Budget Period

Used Downtime

OUTPUT

Client Side

ADVERTISEMENT · REMOVE?

Guide

Uptime / SLA Calculator

Translate any service level agreement target into the precise downtime budget you are allowed across a year, quarter, month, week, day, or hour. The calculator works in three directions: convert an SLA percentage into allowed downtime, work backwards from a downtime ceiling to the SLA percentage you must commit to, and track how much of an active error budget is still available for the current period.

How to Use

Pick a mode at the top: downtime from SLA percentage, required SLA from a target downtime, or remaining error budget.
For downtime mode, choose a common tier (99%, 99.9%, 99.99%, 99.999%) or type any custom percentage with up to six decimal places.
For required-SLA mode, enter the maximum downtime your service can tolerate and the period it must hold across, such as 30 minutes per month.
For error-budget mode, set the SLA, pick the budget period, and enter how much downtime has been consumed so far to see what is left.
The results update live: a headline value, a per-period breakdown, a side-by-side comparison of common SLA tiers, and a visual budget bar where applicable.

Features

Three calculation modes – SLA to downtime, downtime to SLA, and active error budget tracking from a single screen.
Common tier presets – One click for 99%, 99.5%, 99.9%, 99.95%, 99.99%, and 99.999%, plus any custom percentage you type.
Human-readable durations – Results render as “8h 45m 57s” rather than raw seconds so on-call rotas can read them at a glance.
Per-period breakdown – See the same SLA expressed as downtime per year, quarter, month, week, day, and hour at once.
Tier comparison table – Compare the chosen SLA with neighbouring tiers to decide whether the next nine is worth committing to.
Error budget bar – Visual gauge, percentage used, and a clear over-budget warning when remaining downtime is gone.
Standards-aligned math – Uses a 365.25-day Julian year and 30-day month, matching the conventions used by SRE references and incident commanders.
Fully client-side – Calculations run in your browser, so SLA targets and incident numbers never leave your machine.

 FAQ

What is a service level agreement (SLA) percentage?

An SLA percentage describes the fraction of time a service is contractually expected to be available within a defined period. A 99.9 percent SLA over a 30-day month, for example, allows roughly 43 minutes of cumulative downtime. The percentage is always paired with a measurement window because the same percentage maps to very different absolute durations depending on whether you measure across a day, a month, or a year.
How is allowed downtime calculated from an SLA percentage?

Allowed downtime equals the length of the measurement period multiplied by one minus the SLA expressed as a fraction. If the period is 2,592,000 seconds (a 30-day month) and the SLA is 99.95 percent, the downtime budget is 2,592,000 times 0.0005, which is 1,296 seconds or 21 minutes 36 seconds. The formula is deterministic, so any deviation between calculators comes from differing definitions of a month or year, not from rounding.
Why do calculators use 365.25 days for a year?

A 365.25-day year, known as a Julian year, averages out leap years across long-running services and matches the convention used in SRE handbooks and tools such as uptime.is. Using exactly 365 days under-counts the budget by six hours over a four-year leap cycle. The choice rarely matters for short windows like a month, but it can change a five-nines budget by tens of seconds across a year.
What is an error budget?

An error budget is the cumulative downtime an SRE team is allowed to spend before breaching the SLA for a measurement period. Teams treat it like a finite resource: if releases burn through the budget early in the month, change freezes are imposed; if budget remains near the end of the period, more aggressive releases are encouraged. The concept lets engineering and product teams trade reliability against velocity in measurable terms.
What is the difference between SLA, SLO, and SLI?

A service level indicator (SLI) is a specific measurement, such as the percentage of successful requests. A service level objective (SLO) is the internal target for that indicator, typically set tighter than the contractual SLA. The service level agreement (SLA) is the external contract with consequences attached when missed. Error budgets are usually computed against the SLO so that the team has warning room before the contractual SLA is at risk.