Uptime SLA Calculator
Enter an uptime SLA percentage and see exactly how much downtime it permits each day, month, and year. This free online developer calculator runs entirely in your browser — no signup, no data sent anywhere.
Inputs
Results
How It Works (Formula & Method)
Allowed downtime is the period multiplied by (1 − uptime/100). For 99.9% uptime, the downtime fraction is 0.001 — so a 365.25-day year permits 0.001 × 365.25 days ≈ 8.77 hours of outage. The monthly figure uses an average month of 30.44 days.
Worked Example
Below is a worked example using the calculator's default values. The same numbers are pre-filled in the form above so you can press Calculate and see the result without typing anything.
Inputs used:
- Uptime SLA (%): 99.9
With these inputs, the calculator computes the metrics shown in the Results panel. Change any value and press Calculate again to see how the result responds — the live widget and the chart both update instantly.
About the Uptime SLA Calculator
A Service Level Agreement (SLA) often promises uptime as a percentage — "three nines" (99.9%), "four nines" (99.99%), and so on. Those figures sound similar but translate into very different amounts of tolerated downtime. This calculator converts any uptime percentage into concrete downtime budgets per day, month, and year.
Tips & Considerations
- Each additional "nine" cuts allowed downtime by a factor of ten: 99.9% allows ~8.8 h/year, 99.99% allows ~52 min, 99.999% allows ~5 min.
- SLAs usually specify a measurement window (often monthly) — check which window your contract uses, since that defines the real budget.
- Planned maintenance is sometimes excluded from SLA downtime. Read the agreement to see what counts.
Frequently Asked Questions
How much downtime does 99.9% allow?
About 8.77 hours per year, 43.8 minutes per month, or 1.44 minutes per day.
What do "three nines" and "five nines" mean?
"Three nines" is 99.9% uptime; "five nines" is 99.999%. Each extra nine reduces allowed downtime roughly tenfold.
Does the SLA window matter?
Yes. An SLA measured monthly resets the downtime budget every month, while a yearly window pools it. The same percentage can feel very different depending on the window.
What does the Uptime SLA Calculator compute?
The Uptime SLA Calculator takes 1 input value and returns 3 results. Convert an uptime SLA percentage like 99.9% into allowed downtime per day, month, and year.