Quick answer
Allowed downtime = (1 − availability) × period. A 99.9% SLA allows 525.6 minutes a year, 43.2 minutes a month (30 days), 10.08 minutes a week and 86.4 seconds a day.
Enter an availability percentage. The calculator returns the downtime allowed per year, month, week and day.
Related tools: Memory Utilization Calculator: Share of memory in use. Server Uptime Calculator: Uptime percentage from downtime in a period. IP Subnet Calculator: IPv4 network, broadcast, mask and host range from an address and CIDR prefix.
How to use the SLA Availability Calculator
- Enter availability (%) (between 0 and 100).
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Availability | A number, in % | > 0, ≤ 100 |
Formula and method
Formula
downtime = (1 − availability) × period
IEEE-754 double precision; shown to the decimals indicated.
Uses a 365-day year, 30-day month, 7-day week and 24-hour day.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Availability = 99.9.
| Result | Value |
|---|---|
| Downtime per year | 525.6 min/year |
| Per month (30 days) | 43.2 min |
| Per week | 10.08 min |
| Per day | 86.4 s |
Example 2
Inputs: Availability = 99.99.
| Result | Value |
|---|---|
| Downtime per year | 52.56 min/year |
| Per month (30 days) | 4.32 min |
| Per week | 1.01 min |
| Per day | 8.64 s |
Example 3
Inputs: Availability = 99.5.
| Result | Value |
|---|---|
| Downtime per year | 2,628 min/year |
| Per month (30 days) | 216 min |
| Per week | 50.4 min |
| Per day | 432 s |
The first line is the headline result (downtime per year). Below it the sLA Availability Calculator lists per month (30 days), per week and per day, which describe the same case from other angles. IEEE-754 double precision; shown to the decimals indicated.
Each extra nine
Each extra nine cuts allowed downtime tenfold: 99% is 3.65 days a year, 99.99% about 52.6 minutes.
Reading an SLA
Check how the provider measures availability and what credit you get for a breach. 100% allows no downtime and is not realistic.
Turning an SLA into downtime
99.9% leaves 0.1% of a year as downtime: 525.6 minutes, about 8.76 hours. 99% allows 5,256 minutes (87.6 hours) and 99.99% allows 52.56 minutes.
Services that all must be up are multiplied: two dependent 99.9% services give 99.9% × 99.9% = 99.8001% overall. Check how your agreement measures the window and which maintenance is excluded.
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Availability: entering "0" shows "Availability must be greater than 0." beside that field and no result.
Choosing between the SLA Availability Calculator and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [Memory Utilization Calculator](/technology/memory-utilization-calculator/) | used memory and total memory | Memory utilization |
| [Server Uptime Calculator](/technology/server-uptime-calculator/) | downtime and period | Uptime |
| [IP Subnet Calculator](/technology/ip-subnet-calculator/) | iPv4 address and cIDR prefix length | Network |
| [Download Time Calculator](/technology/download-time-calculator/) | file size, size unit and connection speed | Time |
| [Binary Calculator](/technology/binary-calculator/) | first binary number, second binary number and operation | Result |
Background: networking and display
Network speeds are quoted in bits per second and file sizes in bytes, and a byte is 8 bits, so a 100 Mbps link moves at most 12.5 megabytes per second; real throughput is usually below the advertised rate. Pixel density is the diagonal in pixels divided by the diagonal in inches: a 1920×1080 display of 24 inches is about 92 pixels per inch, and a 3840×2160 display of 27 inches about 163.
Assumptions and limitations
- 100% allows no downtime
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for availability to confirm this.
Frequently asked questions
What is 99.5% per year?
99.5% availability allows 0.5% × 8,760 h ≈ 43.8 hours of downtime a year.
What is five nines?
About 5.3 minutes a year.
Do maintenance windows count?
It depends on the SLA: some exclude scheduled maintenance from downtime, so check the definition before comparing providers.
How much downtime does 99.99% allow per year?
About 52.56 minutes (0.01% of 525,600 minutes).
What happens when services depend on each other?
Availabilities multiply, so two required 99.9% services give about 99.8% together.
What does the SLA Availability Calculator calculate?
Allowed downtime for an availability percentage. It returns Downtime per year, Per month (30 days), Per week and Per day.
What formula does the SLA Availability Calculator use?
downtime = (1 − availability) × period. Uses a 365-day year, 30-day month, 7-day week and 24-hour day.
What do I need to enter in the sLA Availability Calculator?
You enter Availability (%).
How is the result rounded or limited?
IEEE-754 double precision; shown to the decimals indicated. 100% allows no downtime.
What is an example of a sLA Availability result?
With availability 99.9, the downtime per year is 525.6 min/year.
Where does the method come from?
The method follows: Availability = uptime ÷ (uptime + downtime), the usual service-level definition; no single standard fixes the measurement window, so confirm it against your own SLA.
Related calculators
- Memory Utilization Calculator — Share of memory in use.
- Server Uptime Calculator — Uptime percentage from downtime in a period.
- IP Subnet Calculator — IPv4 network, broadcast, mask and host range from an address and CIDR prefix.
- Download Time Calculator — Time to download a file at a given speed.
- Binary Calculator — Add, subtract, multiply, divide or apply bitwise operations to binary numbers.
- Hex Calculator — Add, subtract or multiply hexadecimal numbers.
Sources
- Availability = uptime ÷ (uptime + downtime), the usual service-level definition; no single standard fixes the measurement window, so confirm it against your own SLA
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.