What does one hour of downtime really cost you?
Put a number on IT outages, and see how much downtime a 99.9%, 99.99% or 99.999% SLA actually allows.
- Lost revenue & productivity
- SLA downtime table
- Chained services
- Data stays in your browser
| Lost revenue | |
| Lost staff productivity | |
| Recovery costs |
Not counted: lost customers, reputation damage, SLA penalties and fines. These can be larger than the direct cost.
1. Allowed downtime for an SLA
| Period | Allowed downtime | Cost at your rate* |
|---|
*Uses the cost per hour from the "Cost of downtime" tab. Periods: day 24 h, week 7 days, month 30.44 days, quarter 91.31 days, year 365.25 days.
2. Check an outage against your SLA
3. Combined SLA of your setup
Add every service your system needs to work. Copies are identical instances that can take over for each other, such as two servers behind a load balancer.
| Service | SLA % | Copies | Remove |
|---|
Assumes services fail independently and that switching to another copy is automatic. A shared cause, such as one region or one bad deployment, can take every copy down at once.
Two calculators in one
Use the tabs at the top of the calculator to switch between them.
Cost of downtime
Lost revenue, lost staff productivity and recovery costs for an outage of any length.
SLA & allowed downtime
Turn an uptime percentage into real minutes per day, month and year, then check a real outage against your SLA.
Combined SLA
Add each service your system depends on, with any backup copies, to see the real uptime of the whole setup.
What uptime percentages really mean
Allowed downtime for common SLA levels, assuming 24/7 service.
| SLA | Per month | Per year |
|---|---|---|
| 99% (two nines) | 7 h 18 min | 3 d 15 h 40 min |
| 99.5% | 3 h 39 min | 1 d 19 h 50 min |
| 99.9% (three nines) | 43 min 50 sec | 8 h 46 min |
| 99.95% | 21 min 55 sec | 4 h 23 min |
| 99.99% (four nines) | 4 min 23 sec | 52 min 36 sec |
| 99.999% (five nines) | 26 sec | 5 min 16 sec |
How the cost of downtime is calculated
Direct costs we include
- Lost revenue: revenue per business hour × share of sales that stop.
- Lost productivity: employees affected × hourly cost × share of work that stops.
- Recovery: IT time, overtime and outside help.
Costs we leave out
- Lost customers and reputation damage.
- SLA penalties you owe your own customers.
- Compliance fines. These are hard to estimate but often larger than the direct cost.
Frequently asked questions
What is a good SLA for a small business?
For most business websites and cloud apps, 99.9% is the normal minimum. If an hour of downtime costs you more than a better plan would, pay for 99.95% or 99.99%.
Does an SLA mean I get paid for downtime?
Usually you get service credits, a small discount on your next bill, not compensation for your losses. Compare the credit with your cost of downtime.
How do I calculate uptime percentage?
Uptime % = (total time − downtime) ÷ total time × 100. For example, 45 minutes of downtime in an average month of 43,830 minutes gives (43,830 − 45) ÷ 43,830 × 100 = 99.897%, which just misses a 99.9% SLA. The outage check in the calculator does this for you.
How does redundancy change my uptime?
If two copies of a service can each handle the load, the setup is only down when both fail at the same time. Two copies at 99.9% give 1 − (0.001 × 0.001) = 99.9999%. That only holds if they fail independently and switching is automatic, so two copies in the same data center or region give less than the maths suggests.
What is the difference between an SLA, an SLO and an SLI?
An SLI (service level indicator) is what you measure, such as the share of requests that succeed. An SLO (service level objective) is the target you set for it, such as 99.95% a month. An SLA (service level agreement) is the promise in a contract, often set a little looser than the SLO, with service credits if it is missed.
Is my data saved?
No. Everything is calculated in your browser.
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