Uptime & SLA Calculator

Frequently Asked Questions

What is the difference between SLA, SLO, and SLI?

An SLI is a measured metric. An SLO is your internal target. An SLA is an external commitment to customers with penalties for breach, typically set looser than the SLO to provide a safety buffer.

Does slow responses count as downtime?

In many SLA definitions, yes - responses exceeding a latency threshold are counted as failures. Check the specific definition; a common approach counts responses outside a success/latency threshold.

How do I achieve five nines (99.999%)?

Five nines allows only ~5.26 minutes of downtime per year. It requires fully redundant infrastructure, automated failover in seconds, and zero-downtime deployments. It is only cost-effective for systems with catastrophic downtime consequences.

Why use an average month of 43,800 minutes?

Calendar months range from 28-31 days, making consistent comparison difficult. Using 525,600 / 12 = 43,800 minutes per month keeps monthly and annual budgets exactly consistent.

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This calculator provides estimates for informational purposes only. Results are based on assumptions and may not reflect actual outcomes. Consult qualified professionals in relevant fields before making important decisions based on these results.

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How It Works

Service-level agreements are expressed as a percentage of uptime - the famous 'nines'. 99.9% is 'three nines', 99.99% is 'four nines', and each additional nine reduces the allowed downtime by a factor of ten. The percentage alone is abstract; engineers translate it into an error budget: the maximum downtime allowed over a given window.

In SLA mode, enter a target uptime percentage and the calculator returns the allowed downtime per day, week, month (30.42 days average), quarter, and year. In downtime mode, enter how many minutes of actual downtime occurred over a period and it computes the SLA percentage achieved - useful for monthly service reports or post-incident review.

Use Cases

SLA calculations appear throughout site reliability engineering and contract work:

Setting a realistic SLO (service level objective) by working backward from the downtime budget you can actually achieve with your architecture

Evaluating whether a deploy window fits within the remaining monthly error budget

Writing customer-facing SLA contracts with accurate penalty thresholds based on achievable targets

Monthly SLA reporting - converting raw downtime minutes into a percentage for stakeholder communication

Understanding the engineering investment required to move from three nines to four nines by seeing the 10x difference in allowed downtime

Tips

Each additional nine costs roughly 10x the engineering effort and infrastructure redundancy - going from 99.9% to 99.99% is not incremental, it typically requires redundant systems at multiple failure levels.

Planned maintenance windows spend the same error budget as unplanned outages unless your contract explicitly excludes them.

Measure availability at the user-visible layer, not at individual servers. A healthy database with a broken load balancer or misconfigured DNS is still down from the user's perspective.

Set your internal SLO (objective) higher than your external SLA (agreement) - this buffer means you can miss the SLO occasionally without violating the SLA and triggering penalties.

Short measurement windows are stricter - 60 minutes of downtime in a single month is more impactful than the same 60 minutes spread over a year, even if the annual percentage looks acceptable.

FAQ

What is the difference between SLA, SLO, and SLI?

An SLI (service level indicator) is a measured metric like latency or error rate. An SLO (service level objective) is your internal target for that metric. An SLA (service level agreement) is an external commitment to customers, usually with financial penalties for breach, and is typically set looser than the SLO to give you a safety buffer.

Does slow responses count as downtime?

In many SLA definitions, yes - responses exceeding a latency threshold are counted as failures. Check the specific definition in your SLA; a common approach is to define availability as the percentage of requests that return a successful response within a specified latency budget.

How do I achieve five nines (99.999%)?

Five nines allows only about 5.26 minutes of downtime per year. Achieving this requires fully redundant infrastructure with no single point of failure, automated failover measured in seconds, zero-downtime deployments, and extremely disciplined change management. It is only cost-effective for systems where downtime has direct, catastrophic financial or safety consequences.

Why use an average month of 43,800 minutes?

Calendar months range from 28 to 31 days, making consistent monthly comparisons difficult. Using 525,600 / 12 = 43,800 minutes per month keeps monthly and annual budgets exactly consistent. Actual month lengths will vary slightly from this average.

Uptime & SLA Calculator

Frequently Asked Questions

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