What’s the difference between an SLA and an SLO?

An SLA (service level agreement) is typically a contractual promise to customers that may include penalties or service credits if you fail to meet the stated targets. An SLO (service level objective) is an internal reliability goal engineers use to guide design and operations. This calculator works for both as long as you know the uptime percentage you want to analyze.

Can I change the month or year length used in the calculations?

The calculator uses a 30‑day month and a 365‑day year for simplicity. If your contracts or reports use calendar months, 28‑day billing cycles, or include leap years, you can recalculate the minutes in those periods and apply the same downtime fraction formula.

Does scheduled maintenance count against my uptime?

Many SLAs exclude approved maintenance windows from uptime calculations, while others count any downtime regardless of cause. This tool does not attempt to classify downtime—it simply converts uptime percentages into total downtime minutes. Always check your specific contract or policy to see how maintenance is treated.

How much downtime does 99.999% uptime allow?

Using this calculator’s assumptions, 99.999% uptime (five nines) allows about 0.0144 minutes per day, 0.432 minutes per 30-day month, and 5.256 minutes per 365-day year. That is why moving from four nines to five nines is such a major operational step up.

What about partial outages or degraded service?

The calculator assumes a simple up‑or‑down model. In reality, you may have incidents where only part of the functionality is unavailable or performance is degraded. How those situations count toward uptime depends on your monitoring strategy and contractual definitions.

tech calculator

Uptime SLA Calculator

Convert an uptime or availability target into allowed downtime per day, month, and year.

Results

Downtime per day (minutes): 1.44
Downtime per month (minutes): 43.20
Downtime per year (minutes): 525.60

Overview

If someone promises 99.9%, 99.95%, or 99.99% availability, the practical question is how much downtime that actually allows in the period you manage: today, this month, or this year. This uptime SLA calculator turns an abstract uptime target into concrete downtime budgets so engineers, platform teams, buyers, and operators can translate "nines" into minutes and hours they can actually use.

Use it as an availability calculator for reliability planning, vendor comparison, maintenance-window sizing, and stakeholder communication. The math is intentionally simple: convert uptime to a downtime fraction, apply it to a day, a standard 30-day month, and a 365-day year, and then interpret the result as a planning budget rather than a provider-specific contract ruling.

How to use this calculator

Enter the uptime percentage specified in your SLA or internal SLO. Common values include 99%, 99.5%, 99.9% ("three nines"), 99.95%, or 99.99% ("four nines").
Review the resulting downtime minutes per day to understand how much room a single bad incident has before you burn through an entire day’s budget.
Check the downtime per 30‑day month to get a sense for how much cumulative downtime you can afford across all incidents in a typical billing period.
Look at the downtime per 365‑day year to understand the high‑level promise you are making to customers and how that compares to alternative SLA tiers.
Use the numbers to tune alert thresholds, maintenance windows, and on‑call expectations, or to explain SLA trade‑offs to non‑technical stakeholders.

Inputs explained

Target uptime (%): The availability goal you want to analyze, expressed as a percentage between 0 and 100. This can be a customer‑facing SLA in a contract or an internal SLO used for engineering reliability targets. Typical cloud and SaaS SLAs use values such as 99.0, 99.5, 99.9, 99.95, or 99.99.

Outputs explained

Downtime per day (minutes): The maximum amount of downtime you can incur in a single 24‑hour day while still hitting the target uptime. This is helpful when designing incident response policies or understanding how severe a given outage is relative to your daily budget.
Downtime per month (minutes): The allowed downtime over a 30‑day month. Many contracts and cloud pricing pages quote monthly SLAs, so this number makes it easier to compare providers or assess whether a cluster of incidents in one month has pushed you over budget.
Downtime per year (minutes): The total downtime budget over a 365‑day year implied by your uptime target. This figure is useful for executive‑level reporting and for sanity‑checking whether a proposed SLA is realistic given your architecture and operational maturity.

How it works

You provide a target uptime percentage such as 99%, 99.5%, 99.9%, or 99.99%. We first convert that uptime into a downtime fraction by computing 1 − (uptime ÷ 100). For example, 99.9% uptime corresponds to 0.1% downtime, or a downtime fraction of 0.001.

Next, we multiply that downtime fraction by the total number of minutes in each period we report. For a calendar day we assume 24 hours × 60 minutes = 1,440 minutes; for a standard 30‑day month we use 30 × 1,440 = 43,200 minutes; for a 365‑day year we use 365 × 1,440 = 525,600 minutes.

For each period (day, month, year) we compute DowntimeMinutes = DowntimeFraction × MinutesInPeriod, then round to a sensible number of decimal places so the results are easy to read in runbooks and dashboards.

Because teams often like to think in hours or seconds, you can mentally convert the minute outputs into hours (divide by 60) or seconds (multiply by 60). The examples in this tool and the copy on the page highlight common SLA tiers such as 99.9% and 99.99% to make the numbers feel concrete.

The underlying math is deliberately simple and deterministic. There is no stochastic modeling or distribution of incidents over the year—this calculator just tells you, if you miss your target by exactly the allowed amount, how many minutes of downtime that corresponds to across different time scales.

Formula

Let U be the uptime target expressed as a percentage (for example, U = 99.9).

1. Convert uptime to a downtime fraction:
   DowntimeFraction = 1 − (U ÷ 100).

2. Compute minutes in each period:
   MinutesPerDay   = 24 × 60 = 1,440.
   MinutesPerMonth = 30 × 1,440 = 43,200 (standard 30‑day month).
   MinutesPerYear  = 365 × 1,440 = 525,600.

3. Downtime budgets (in minutes):
   DayDowntime   = DowntimeFraction × MinutesPerDay.
   MonthDowntime = DowntimeFraction × MinutesPerMonth.
   YearDowntime  = DowntimeFraction × MinutesPerYear.

You can convert any of these minute values to hours by dividing by 60, or to seconds by multiplying by 60.

When to use it

Translating abstract "three‑nines" or "four‑nines" commitments into concrete downtime budgets that engineers, managers, and customers can understand quickly.
Checking whether a planned maintenance window, migration, or outage review would consume too much of the monthly downtime budget.
Comparing reliability tiers such as 99.9%, 99.95%, and 99.99% when evaluating cloud, infrastructure, or SaaS vendors.
Setting or reviewing internal SLOs so they leave enough room to comfortably meet customer-facing SLA promises.
Explaining to non-technical stakeholders why a small percentage change in uptime can dramatically tighten the tolerated downtime.

Tips & cautions

If you want results in hours instead of minutes, divide the outputs by 60; if you need seconds for alerting thresholds or synthetic checks, multiply by 60.
Align the 30‑day month assumption with your billing or reporting period. For example, if your contracts reference calendar months, you may want to recompute using 28, 30, or 31 days depending on the specific month.
Use this tool alongside request‑based error budgets (for example, 99.9% of requests must succeed) to get a full picture of reliability. Time‑based and request‑based SLAs emphasize different dimensions of reliability.
When presenting results to non‑technical stakeholders, highlight the yearly downtime figure in hours. It is often easier to say "about 8.8 hours per year" than to discuss fractions of a percent.
Re‑run the calculator with slightly higher or lower uptime targets to show how much tougher it is to move from, say, 99.9% to 99.99% in terms of allowable downtime.
Uses a simple 30‑day month and 365‑day year. If your contracts reference calendar months, leap years, or custom reporting periods, you should recompute the minutes for those exact periods.
Does not distinguish planned versus unplanned downtime. Many SLAs exclude scheduled maintenance windows, so you may need to track those separately when applying these budgets.
Focuses purely on time‑based availability and does not include request‑level error rates, partial degradations, or performance‑related SLOs such as latency and throughput.
Treats uptime as a single aggregate number over the period. In reality, customer impact depends heavily on when downtime occurs (for example, peak hours vs overnight) and which capabilities are affected.
Does not calculate financial penalties, service credits, or other business terms that might be triggered by SLA breaches; you must apply your contract language to the downtime numbers provided.

Worked examples

Example 1: 99.9% uptime (three nines)

Target uptime U = 99.9%. DowntimeFraction = 1 − (99.9 ÷ 100) = 1 − 0.999 = 0.001.
Per day: 0.001 × 1,440 minutes ≈ 1.44 minutes of allowable downtime per 24‑hour day.
Per month (30 days): 0.001 × 43,200 minutes ≈ 43.2 minutes of downtime per 30‑day month.
Per year (365 days): 0.001 × 525,600 minutes ≈ 525.6 minutes ≈ 8.76 hours of downtime per year.
Interpretation: a single 30‑minute incident in a month would consume a large share of your monthly error budget at 99.9% uptime.

Example 2: 99.99% uptime (four nines)

Target uptime U = 99.99%. DowntimeFraction = 1 − (99.99 ÷ 100) = 0.0001.
Per day: 0.0001 × 1,440 minutes ≈ 0.144 minutes ≈ 8.64 seconds of allowable downtime per day.
Per month (30 days): 0.0001 × 43,200 minutes ≈ 4.32 minutes of downtime per 30‑day month.
Per year (365 days): 0.0001 × 525,600 minutes ≈ 52.56 minutes of downtime per year.
Interpretation: moving from 99.9% to 99.99% uptime cuts the annual downtime budget from roughly 8.8 hours to under an hour, dramatically increasing the reliability bar.

Example 3: A 20-minute maintenance window against a 99.95% monthly target

Target uptime U = 99.95%. DowntimeFraction = 1 − (99.95 ÷ 100) = 0.0005.
Per month (30 days): 0.0005 × 43,200 minutes = 21.6 minutes of allowable downtime for the month.
If one planned maintenance window lasts 20 minutes, it consumes 20 ÷ 21.6 ≈ 92.6% of the full monthly downtime budget.
Interpretation: even when the percentage looks generous, a single maintenance event can use almost the entire monthly allowance at higher availability tiers.

Deep dive

This uptime SLA calculator converts availability targets such as 99%, 99.5%, 99.9%, 99.95%, and 99.99% into concrete downtime budgets per day, month, and year. Instead of guessing what "three nines" or "four nines" mean, you can see exactly how many minutes of downtime are implied by the target.

Use it as an availability calculator when you need to answer questions like "how much downtime is 99.99% per month?" or "will this maintenance window burn most of our monthly budget?" The outputs make reliability targets easier to use in planning, vendor comparison, and post-incident discussions.

Enter the uptime percent from your SLA or SLO to see the implied downtime in minutes for a 24-hour day, a standard 30-day month, and a 365-day year. Small changes in uptime percentage create big changes in allowable downtime, especially once you move into four or five nines.

Because the calculator uses transparent percentage math and fixed period lengths, it works well as a fast planning tool during design reviews, platform conversations, or procurement discussions. Use the numbers as a starting point, then apply your actual contract language and measurement rules before making formal commitments.

Methodology & assumptions

The calculator reads a single uptime input and clamps it to a percentage between 0 and 100; the default example value is 99.9.
It converts uptime to a downtime fraction using DowntimeFraction = 1 − (UptimePercent ÷ 100).
It treats one day as 1,440 minutes (24 × 60), one month as 43,200 minutes (30 × 1,440), and one year as 525,600 minutes (365 × 1,440).
Downtime per day, month, and year are each calculated by multiplying the downtime fraction by the number of minutes in the relevant period.
The route models time-based availability only. It does not weight requests, traffic volume, geography, service exclusions, or provider-specific service-credit rules.
The 30-day month and 365-day year are fixed planning assumptions so the numbers stay comparable across common uptime tiers like 99.9%, 99.95%, 99.99%, and 99.999%.
Results are displayed as planning estimates. If a contract measures uptime over calendar months, excludes maintenance, or uses a custom definition of downtime, the same formula should be rerun with those exact rules.
Copy on the page is kept in sync with the route computation implemented in `uptimeSlaCalculator` so the formula, examples, and outputs describe the same logic.

Sources

Google Cloud Blog — SRE fundamentals: SLIs vs SLAs vs SLOsUsed for the route’s distinction between SLOs, SLAs, and availability targets.
Google SRE Book — Embracing RiskExplains time-based availability, common 'nines,' and how uptime targets map to downtime/error budgets.
BIPM — SI BrochureAuthoritative reference for the time units used when expressing downtime outputs in minutes, hours, days, and years.

FAQs

What’s the difference between an SLA and an SLO?: An SLA (service level agreement) is typically a contractual promise to customers that may include penalties or service credits if you fail to meet the stated targets. An SLO (service level objective) is an internal reliability goal engineers use to guide design and operations. This calculator works for both as long as you know the uptime percentage you want to analyze.
Can I change the month or year length used in the calculations?: The calculator uses a 30‑day month and a 365‑day year for simplicity. If your contracts or reports use calendar months, 28‑day billing cycles, or include leap years, you can recalculate the minutes in those periods and apply the same downtime fraction formula.
Does scheduled maintenance count against my uptime?: Many SLAs exclude approved maintenance windows from uptime calculations, while others count any downtime regardless of cause. This tool does not attempt to classify downtime—it simply converts uptime percentages into total downtime minutes. Always check your specific contract or policy to see how maintenance is treated.
How much downtime does 99.999% uptime allow?: Using this calculator’s assumptions, 99.999% uptime (five nines) allows about 0.0144 minutes per day, 0.432 minutes per 30-day month, and 5.256 minutes per 365-day year. That is why moving from four nines to five nines is such a major operational step up.
What about partial outages or degraded service?: The calculator assumes a simple up‑or‑down model. In reality, you may have incidents where only part of the functionality is unavailable or performance is degraded. How those situations count toward uptime depends on your monitoring strategy and contractual definitions.

Related calculators

tech

Video Streaming Bandwidth Calculator

Estimate video bandwidth and daily data usage by resolution, FPS, stream count, and hours per day.

tech

Download Time Calculator

Estimate file transfer time from file size and Mbps in seconds, minutes, and hours.

tech

Upload Time Calculator

Estimate file upload time from file size and upstream Mbps in seconds, minutes, and hours.

This uptime SLA calculator is an educational planning tool that converts availability percentages into approximate downtime budgets using fixed 30‑day months and 365‑day years. It does not implement provider‑specific SLA rules, definitions of "downtime," or financial penalty calculations. Always refer to your actual contracts and internal policies when making reliability commitments or assessing whether a service has met its formal obligations.