How do you calculate availability?

Availability (%) = (Total Time − Downtime) / Total Time × 100. For example, a service that was down 7.3 hours in a 30-day month (720 hours) has an availability of (720 − 7.3) / 720 × 100 = 98.99%.

How much downtime does 99.95% uptime allow?

At 99.95% uptime, the maximum allowed downtime is 43 seconds per day, 21 minutes 36 seconds per 30-day month, and 4 hours 22 minutes 48 seconds per 365-day year.

What's the difference between 99.9% and 99.99% uptime?

Each additional nine reduces allowed downtime tenfold: 99.9% allows about 8 hours 46 minutes of downtime per year, while 99.99% allows just under 53 minutes. Meeting 99.99% generally requires automated failover, since a human response rarely fits inside the budget.

How do I track SLA compliance?

Continuous uptime monitoring measures availability from outside your infrastructure and records every outage. Hyperping checks your endpoints at up to 30-second intervals from multiple regions and reports uptime, MTTR, and SLA compliance over any period.

What SLA percentage should I enter in the calculator?

Enter the uptime target written in your SLA, such as 99.9% or 99.99%. If you are comparing targets, try each percentage and choose a downtime budget your service can meet consistently.

SLA & Uptime Calculator: 99.9%, 99.99% or Any % to Downtime

How to use this SLA calculator

Enter an uptime percentage, or start from a preset, and the calculator converts it into concrete allowances per day, week, 30-day month, quarter, and 365-day year. The arithmetic is one line: allowed downtime = period length × (1 − SLA ÷ 100). A 30-day month at 99.5% works out to 2,592,000 seconds × 0.005, or 3 hours 36 minutes, which is usually a good deal more than the number sounded like.

When you choose a level to commit to, work backwards from your track record: pull the last twelve months of uptime data, find your worst month, and set the SLA one notch below what you actually achieved. Promising more than you have historically delivered is how service-credit clauses get expensive.

Your error budget: 21m 36s a month.

Get paged the second you start spending it.

An SLA is a promise. Who tells you when you break it?

Hyperping checks every 30 seconds from 18 locations and alerts you before the budget is gone: Slack, SMS, phone call, PagerDuty.

Free plan · no credit card · first check in under a minute

Enter an endpoint. The first check runs in under a minute.

Promising 99.95% to customers? Show it on a status page they can see, from $29/mo with monitoring included →

What the percentage leaves out

Two definitions decide more than the arithmetic does. The first is what counts as downtime: a checkout that loads but cannot take payments is down in every way that matters, so measure availability against user-facing transactions rather than infrastructure heartbeats. The second is the measurement window. The same figure evaluated per year lets a vendor bank good months against one terrible day, while a monthly window caps what any single incident can hide.

Exclusions and maintenance carve-outs finish the job. Before comparing two vendors on their percentages, read the remedy schedule, the window, and the carve-outs, then ask for the incident history that backs the number. A published percentage with no status page and no historical data is a marketing claim, not a measurement.

Past five nines, the promise stops being measurable at all

Calculate achieved availability from incidents

For historical performance, add the duration of every user-visible incident, merge overlapping intervals, then divide available time by the full measurement window. Availability (%) = (total time minus downtime) divided by total time, multiplied by 100.

Keep partial degradation rules consistent. If half of requests failed for ten minutes, decide whether the SLA counts ten minutes of outage or five weighted minutes, document that rule, and apply it to every report.

Choose a user-visible availability signal

Monitor the action customers need to complete, not just the host that serves it. An HTTP check can validate status, latency, and response content, while a browser flow can confirm that a login, checkout, or dashboard works end to end.

Run the signal from more than one region and confirm a failure before opening an incident. This distinguishes a real service outage from a local network problem without reducing availability to an internal heartbeat.

Compare SLA tiers by business impact

Convert each candidate percentage into minutes, then multiply those minutes by the revenue, support load, or operational cost of an outage. That makes the value of moving from one tier to the next visible in the same units as the engineering price.

Set the target where the avoided loss justifies the added redundancy and response work. A higher percentage is not automatically better if users can tolerate the interruption and the extra architecture costs more than it protects.

Budgeting for downtime

Every uptime target implies a downtime budget (the amount of failure you’re allowed before breaching it). This calculator shows the budget for any percentage: at 99.9% you get 43 minutes 12 seconds per 30-day month; at 99.99%, just 4 minutes 19 seconds.

Mature teams treat that budget as a resource to spend deliberately on deploys, migrations, and controlled risk, rather than as an emergency reserve. If you’re consistently under budget, you can ship faster; if you’re over, reliability work jumps the queue.

Match the calculator to the contract window

A fixed 30-day month, a calendar month, and a rolling 30-day window produce different allowances and reset at different times. Annual calculations also need the contract’s rule for leap years and partial service periods.

Use the same boundary when comparing the calculator with a vendor report. Otherwise a failure near midnight or month-end can be allocated to different windows, making two correct calculations appear to disagree.

Turn the result into an enforceable SLA

Write down the monitored service, the successful response criteria, the observation locations, and the source of truth for incident duration. Without those fields, two parties can calculate different uptime from the same outage.

Tie remedies to explicit thresholds and require prompt incident notification plus access to historical measurements. The calculator supplies the time limits; the contract must say how a breach is proven and what happens next.

Downtime allowed at each SLA level

Uptime	Per day	Per month	Per year
99% Two nines	14m 24s	7h 12m	3d 15h
99.9% Three nines	1m 26s	43m 12s	8h 45m 36s
99.95%	43s	21m 36s	4h 22m 48s
99.99% Four nines	9s	4m 19s	52m 34s
99.999% Five nines	864ms	26s	5m 15s
99.9999% Six nines	86ms	3s	32s
99.9999999% Nine nines	86μs	2.6ms	32ms

SLA calculation cheatsheet

Availability calculation

Availability (%) = (Total Time - Downtime) / Total Time × 100

Example: If a service was down for 7.3 hours in a 30-day month:

Total Time = 30 days × 24 hours = 720 hours
Availability = (720 - 7.3) / 720 × 100 = 98.99%

Response time SLA

Response Time Compliance (%) = (Responses Within Threshold / Total Responses) × 100

Mean time metrics

MTBF (Mean Time Between Failures) = Total Operational Time / Number of Failures
MTTR (Mean Time To Repair) = Total Repair Time / Number of Repairs
MTTA (Mean Time To Acknowledge) = Total Time to Acknowledge / Number of Incidents

Service credit calculation

Service Credit = (Monthly Service Fee) × (Credit Percentage for SLA Breach)

SLA penalty example

If availability drops below 99.9% but remains above 99.0%: 10% credit
If availability drops below 99.0%: 25% credit

Track SLAs and downtime metrics at a glance

Hyperping reports on service reliability using data collected by your monitors. Select the reporting period, then review the results in the dashboard or export them.

Track uptime, Mean Time to Recovery (MTTR), and SLA compliance for any reporting period.
Export the selected period as a CSV file for audits, client reports, spreadsheets, or internal analysis.
Review the complete incident history and use filters to narrow the records included in your report.

Monitor reporting dashboard showing outages, MTTR, and SLA metrics over time →

Monitor reporting analytics — Monitor reporting dashboard showing outages, MTTR, and SLA metrics over time →

SLA & uptime management guides

Incident Management: Best Practices, Tools Guide & MoreIn this guide, we'll walk through everything you need to know about incident management, from basic concepts to advanced strategies used by top DevOps teams.Understanding SLAs, SLOs, and SLIsSLAs, SLOs, and SLIs are crucial for managing tech services, ensuring reliability and trust. Learn how these elements work together to maintain service quality and user satisfaction.MTTR guide: how to improve system reliability & response timeMeantime to repair (MTTR) directly impacts your customer trust and company reputation. This guide provides actionable steps to boost your system reliability and keep customers happy.

What is uptime?

Uptime is the amount of time that a service is available and operational, typically expressed as a percentage over a given period such as a month or a year.

What is an SLA?

A service-level agreement (SLA) defines the level of service you expect from a vendor, laying out the metrics by which service is measured, as well as remedies or penalties should agreed-on service levels not be achieved.

How to prevent downtime?

Redundancy, monitoring and alerting are key to ensure a safe and reliable service.

Frequently asked questions

How do you calculate availability?: Availability (%) = (Total Time − Downtime) / Total Time × 100. For example, a service that was down 7.3 hours in a 30-day month (720 hours) has an availability of (720 − 7.3) / 720 × 100 = 98.99%.
How much downtime does 99.95% uptime allow?: At 99.95% uptime, the maximum allowed downtime is 43 seconds per day, 21 minutes 36 seconds per 30-day month, and 4 hours 22 minutes 48 seconds per 365-day year.
What's the difference between 99.9% and 99.99% uptime?: Each additional nine reduces allowed downtime tenfold: 99.9% allows about 8 hours 46 minutes of downtime per year, while 99.99% allows just under 53 minutes. Meeting 99.99% generally requires automated failover, since a human response rarely fits inside the budget.
How do I track SLA compliance?: Continuous uptime monitoring measures availability from outside your infrastructure and records every outage. Hyperping checks your endpoints at up to 30-second intervals from multiple regions and reports uptime, MTTR, and SLA compliance over any period.
What SLA percentage should I enter in the calculator?: Enter the uptime target written in your SLA, such as 99.9% or 99.99%. If you are comparing targets, try each percentage and choose a downtime budget your service can meet consistently.