SysAdmin Tools

SLA Uptime Calculator

Calculate the exact downtime any uptime percentage allows — per day, week, month, quarter and year. Compare SLA tiers and generate ready-to-paste clause text.

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Quick pick

Downtime allowed at 99.9%

Under 1 day of downtime per year
PeriodDowntime Allowed
Per day0h 1min 26sec
Per week0h 10min 5sec
Per month0h 43min 50sec
Per quarter2h 11min 29sec
Per year8h 45min 58sec

Ready-to-paste SLA clause

Service provider guarantees 99.9% uptime measured monthly, allowing maximum 44 minutes downtime per month.

Compare all SLA tiers

SLAPer dayPer weekPer monthPer quarterPer year
99%14m 24s1h 40m7h 18m21h 54m87h 39m
99.5%7m 12s50m 24s3h 39m10h 57m43h 49m
99.9%1m 26s10m 5s43m 50s2h 11m8h 45m
99.95%43s5m 2s21m 55s1h 5m4h 22m
99.99%9s1m 0s4m 23s13m 9s52m 36s
99.999%1s6s26s1m 19s5m 16s

What each tier means

Calculated in your browser using a 365.25-day year. Nothing is sent to any server.

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This uptime calculator turns an abstract availability percentage into the concrete downtime it allows — in hours, minutes and seconds per day, week, month, quarter and year. Type any uptime percentage such as 99.9, or tap a preset like 99.99%, and the numbers update instantly. Everything runs in your browser as pure math, so there is no signup, no tracking and no data leaves your device.

Availability figures are deceptively small. The gap between 99.9% and 99.99% looks like a rounding error, yet it is the difference between roughly 8.8 hours and 52 minutes of permitted downtime per year. When you are negotiating a service level agreement, comparing hosting providers, or writing an SLA clause for a client, seeing the real downtime allowance side by side removes the guesswork. This SLA calculator and availability calculator is built for exactly that — freelancers scoping a support contract, sysadmins sizing a maintenance window, and buyers sanity-checking a hosting uptime guarantee.

Use it as a 99.9 uptime downtime calculator to justify a maintenance window, as a comparison sheet across all six common tiers, or as a one-click generator for ready-to-paste contract language. The comparison table lays out 99% through the coveted five nines (99.999%) so the value of each extra nine is obvious at a glance.

How to Use the SLA Uptime Calculator

  1. 1

    Enter an uptime percentage

    Type any availability figure into the large input — for example 99.9 — or click one of the quick-pick pills (99%, 99.5%, 99.9%, 99.95%, 99.99%, 99.999%) to fill it instantly. The results recalculate in real time as you type.

  2. 2

    Read the downtime table

    The results table shows the maximum downtime that percentage permits per day, week, month, quarter and year. The values are colour-coded green, amber or red so you can judge the SLA quality at a glance against the yearly allowance.

  3. 3

    Compare all six SLA tiers

    The comparison table lists 99%, 99.5%, 99.9%, 99.95%, 99.99% and 99.999% side by side. This is ideal for client proposals — it makes the difference between "three nines" and "four nines" immediately tangible.

  4. 4

    Generate an SLA clause

    Click "Generate SLA Clause" to produce ready-to-paste contract text stating the guaranteed uptime and the maximum monthly downtime in minutes. Copy it straight into your agreement, statement of work, or proposal.

Understanding Uptime, Downtime and Availability

Uptime is the proportion of time a service is operational and reachable, expressed as a percentage of a measurement period. Downtime is the complement — the time the service is unavailable. Because the two always sum to 100%, downtime is simply (1 − uptime%) × period length. A 99.9% monthly SLA therefore permits 0.1% of about 30.44 days, which is roughly 43.8 minutes per month. The phrase "number of nines" is shorthand for these tiers: two nines is 99%, three nines is 99.9%, four nines is 99.99%, and five nines is 99.999% — the gold standard for high availability and mission-critical systems. Each additional nine cuts the allowed downtime by a factor of ten, which is why the cost of infrastructure rises sharply as you climb the ladder. Two related metrics often appear alongside availability in a cloud SLA. MTBF (mean time between failures) measures how often outages occur, while MTTR (mean time to repair) measures how quickly service is restored. Availability can be expressed as MTBF ÷ (MTBF + MTTR), which is why reducing repair time is often the cheapest route to a better uptime figure. This calculator uses a 365.25-day year and derives the month and quarter from it, so every period stays internally consistent.
FieldDescription
99% (two nines)About 3.65 days of downtime per year. Typical of basic shared hosting with no formal guarantee.
99.9% (three nines)About 8.8 hours per year, or ~43.8 minutes per month. The standard business SLA baseline.
99.95%About 4.4 hours per year. Common for premium hosting and managed services.
99.99% (four nines)About 52.6 minutes per year. Enterprise-grade availability for revenue-critical systems.
99.999% (five nines)About 5.3 minutes per year. Mission-critical, high-availability infrastructure with redundancy at every layer.

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Who Uses an SLA Uptime Calculator

Freelancers and agencies

Scope a realistic support contract by translating a promised uptime percentage into a concrete downtime allowance. Generate the SLA clause text and paste it directly into your statement of work so both sides know exactly what "99.9% uptime" costs in minutes.

Sysadmins and DevOps

Size a maintenance window against the SLA budget. If your monthly allowance is 43.8 minutes at 99.9%, a 30-minute deploy leaves little room for error — the calculator makes that tradeoff explicit before you schedule the change.

Buyers comparing providers

A hosting uptime guarantee of 99.95% versus 99.99% sounds trivial until you see 4.4 hours against 52 minutes per year. Use the comparison table to hold vendors accountable and pick the tier your business actually needs.

Product and finance teams

Model the business impact of an availability target. Pair the downtime figures with your revenue-per-hour to estimate the cost of each SLA tier, and decide whether the jump to five nines is worth the infrastructure investment.

SLA Uptime Calculator — Frequently Asked Questions

What does 99.9% uptime mean?
99.9% uptime — often called "three nines" — means a service is guaranteed to be available 99.9% of the measurement period, leaving 0.1% for downtime. Over a 365.25-day year that works out to roughly 8.8 hours of permitted downtime, about 43.8 minutes per month, or just under 10.1 minutes per week. It is the most common baseline in business hosting and SaaS service level agreements, striking a practical balance between reliability and cost.
How much downtime is 99.99% uptime per year?
99.99% uptime, or "four nines", allows 0.01% downtime. Across a 365.25-day year that is about 52.6 minutes — roughly 4.4 minutes per month and around 13 minutes per quarter. This enterprise-grade tier is typical for revenue-critical applications, payment systems and popular SaaS platforms. Hitting it reliably usually requires redundant infrastructure, automated failover and a low mean time to repair, since a single lengthy incident can exhaust the entire annual budget.
What is the difference between 99.9% and 99.99% uptime?
The extra nine reduces allowed downtime by a factor of ten. 99.9% permits about 8.8 hours of downtime per year, while 99.99% permits only about 52.6 minutes. Per month the gap is roughly 43.8 minutes versus 4.4 minutes. Although the percentages look almost identical, the operational difference is enormous: four nines typically demands redundancy, automated failover and rapid incident response, which is why it costs substantially more to guarantee than three nines.
What is a good uptime SLA?
It depends on how much an outage costs you. 99.9% is a solid, widely accepted baseline for most business websites and internal applications. Customer-facing or revenue-generating systems often target 99.95% or 99.99%. Only mission-critical infrastructure — payment networks, emergency services, core telecoms — justifies the cost of 99.999%. A "good" SLA is one whose downtime allowance is smaller than the disruption your business can absorb, balanced against the price of the extra reliability.
What does five nines uptime mean?
Five nines means 99.999% availability, allowing just 0.001% downtime. Over a full year that is only about 5.3 minutes, roughly 26 seconds per month. It represents the gold standard for high-availability systems and is famously associated with carrier-grade telecom equipment. Achieving five nines requires redundancy at every layer — power, network, storage and compute — plus automated failover and near-instant recovery, because even one modest outage would blow the entire yearly budget.
How do cloud providers calculate uptime?
Cloud providers typically define uptime as the percentage of minutes in a billing month during which the service was available, excluding scheduled maintenance and events outside their control. The formula is (total minutes − downtime minutes) ÷ total minutes × 100. Many SLAs use "unavailable" thresholds — for example, an error rate above a set percentage counts as downtime. If the provider misses the committed figure, you usually claim service credits rather than a cash refund.
How do I write an uptime SLA for clients?
State the guaranteed uptime percentage, the measurement period (usually monthly), what counts as downtime, and any exclusions such as scheduled maintenance. Then translate the percentage into a concrete downtime allowance so expectations are unambiguous. This tool's "Generate SLA Clause" button produces ready-to-paste text: it names the percentage and the maximum permitted minutes of downtime per month. Add a remedy — typically service credits — and define how availability will be measured and reported.
What is downtime and how is it measured?
Downtime is any period during which a service is unavailable or fails to meet its agreed performance threshold. It is usually measured with external monitoring that probes the service at regular intervals; consecutive failed checks are logged as an outage. Downtime is expressed as minutes per period or as the complement of uptime — (1 − uptime%) × period length. SLAs often exclude planned maintenance windows and force-majeure events from the measured total.
Can I claim compensation if my host misses the SLA?
Usually, but the remedy is defined by the SLA itself. Most providers offer service credits — a percentage of your monthly fee refunded as account credit — rather than cash compensation for lost business. The credit typically scales with how far availability fell below target. You generally must request the credit within a set window and provide evidence from your own monitoring. Always read the exclusions, because scheduled maintenance and third-party failures are often carved out.
What is the difference between availability and uptime?
In everyday use the terms are interchangeable, and this calculator treats them as the same. Strictly, uptime is the raw time a system is powered on and running, while availability is the proportion of time it is actually able to serve requests correctly, factoring in performance and reachability. A server can be "up" yet unavailable if it is overloaded or unreachable. SLAs almost always specify availability, since that reflects the user's real experience.

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