—
SLA Uptime Calculator — Convert Any Availability Percentage Into Real Downtime
An SLA figure like 99.9% sounds reassuring until you convert it into actual minutes. This free SLA uptime calculator translates any availability commitment into the downtime it permits per day, week, month, quarter and year — and works in reverse, so you can enter an outage you actually suffered and find out whether your provider breached contract. Everything runs in your browser; nothing is uploaded.
What the “nines” actually buy you
Each additional nine reduces permitted downtime roughly tenfold, and the jump in engineering cost between tiers is steep. The table below assumes a 365-day year and a 30-day month, the conventions used by most commercial contracts.
| Availability | Per month (30 days) | Per year (365 days) | Typically seen in |
|---|---|---|---|
| 99% | 7h 12m | 3d 15h 36m | Internal tools, free tiers |
| 99.5% | 3h 36m | 1d 19h 48m | Entry-level shared hosting |
| 99.9% | 43m 12s | 8h 45m 36s | Standard business SaaS |
| 99.95% | 21m 36s | 4h 22m 48s | Paid cloud compute tiers |
| 99.99% | 4m 19s | 52m 34s | Enterprise, financial services |
| 99.999% | 26s | 5m 15s | Telecom, core infrastructure |
How the calculation works
Permitted downtime is simply the length of the measurement period multiplied by the complement of the availability figure: downtime = period × (100 − SLA) / 100. A 30-day month contains 2,592,000 seconds, so a 99.9% SLA permits 2,592,000 × 0.001 = 2,592 seconds, or 43 minutes 12 seconds. The calculator also shows an average-length month of 30.44 days, because some providers measure calendar months rather than fixed 30-day windows — a difference that matters when you are close to the threshold.
Reverse mode: did your provider breach the SLA?
Switch to Downtime → Achieved, enter the outage duration and the period it fell within, and the tool returns the availability percentage you actually received, together with how much downtime budget remained or was exceeded. This is the number to quote when claiming service credits. Note that most contracts exclude scheduled maintenance windows from the calculation, so subtract any planned downtime before entering your figure.
Things contracts hide in the fine print
- Measurement window. Monthly measurement is far more forgiving to a provider than annual, because a single bad month cannot be averaged away across the year.
- Exclusions. Scheduled maintenance, force majeure, third-party network faults and customer-side misconfiguration are usually carved out.
- Service credits are capped. Compensation is typically a percentage of the monthly fee, not your actual business loss, and is often capped at 100% of that month.
- You usually have to claim. Credits are rarely automatic and often expire within 30 days of the incident.
- Composite availability. Chaining four 99.9% services in series gives roughly 99.6% end-to-end, not 99.9%. Multiply the decimals to see your real exposure.
Frequently asked questions
How much downtime does a 99.9% SLA allow?
A 99.9% SLA permits 43 minutes 12 seconds of downtime in a 30-day month, and 8 hours 45 minutes 36 seconds across a 365-day year. Per week it allows 10 minutes 5 seconds, and per day 1 minute 26 seconds.
What is the difference between 99.9% and 99.99% uptime?
Adding one nine cuts permitted downtime by a factor of ten. 99.9% allows about 43 minutes a month; 99.99% allows about 4 minutes 19 seconds. The engineering cost of that extra nine is usually substantial, requiring redundancy across zones and automated failover.
Does scheduled maintenance count against an SLA?
In most commercial contracts it does not. Providers typically exclude announced maintenance windows from availability calculations, which is why measured uptime and contractual uptime can differ. Check the exclusions clause before claiming a breach.
How do I calculate combined uptime across multiple services?
For services in series, multiply their availability decimals: three components at 99.9% each give 0.999 × 0.999 × 0.999 = 99.7% overall. Dependencies compound, so an architecture is only as available as the product of its critical path.
Is this SLA calculator free and private?
Yes. It is completely free, requires no sign-up, and performs every calculation locally in your browser using JavaScript. No figures you enter are transmitted to any server.
Related tools: SaaS Cost Calculator, Subscription Creep Calculator, and Password Strength Analyzer. For infrastructure buying decisions, read our honest reviews.