Uptime & SLA Calculator
See how much downtime an uptime percentage (like 99.9%) actually allows per day, month, and year.
| Period | Allowed downtime |
|---|---|
| Day | 1m 26s |
| Week | 10m 5s |
| Month | 43m 50s |
| Year | 8h 45m 58s |
What is Uptime & SLA Calculator?
An uptime or SLA (Service Level Agreement) percentage like "99.9%" sounds almost identical to "99.99%", but the actual downtime those two numbers allow is very different — and it's rarely obvious just from looking at the percentage. This calculator converts a target uptime percentage into the concrete amount of downtime it permits per day, week, month, and year, so you can sanity-check an SLA you're signing, compare hosting providers, or understand what a status page's historical uptime number actually meant in practical terms. Enter any percentage from 0 to 100, or pick one of the industry-standard "nines" tiers, and the allowed downtime for each period updates instantly.
How to Use Uptime & SLA Calculator
- Type a target uptime percentage into the field (e.g. 99.9), or click one of the preset tier buttons (99%, 99.9%, 99.99%, etc.).
- Read the allowed downtime for that percentage across four periods: day, week, month, and year.
- Compare two SLAs by switching the percentage back and forth and watching how much the allowed downtime changes.
- Use the monthly and yearly figures when evaluating a vendor's SLA credit terms, which are usually expressed per billing period.
Examples
The classic "three nines"
Input: 99.9%
Output: Allows about 1m 26s of downtime per day, and about 8h 45m 58s per year
The classic "two nines"
Input: 99%
Output: Allows about 14m 24s of downtime per day — over 3.5 days per year
Common Mistakes
- Comparing two uptime percentages by eye and assuming the difference is small — 99.9% vs 99.95% looks tiny but is a 2x difference in allowed downtime.
- Using calendar-specific month/year lengths (e.g. exactly 30 days, exactly 365 days) instead of the standard averages SLAs are actually built on, leading to figures that don't match a vendor's own numbers.
- Forgetting that an SLA's downtime definition may exclude scheduled maintenance, meaning actual unplanned-downtime budget can be smaller than the raw percentage implies.
- Treating a single month's or year's actual observed uptime as directly comparable to an SLA target without accounting for how that period's real duration differs from the standard average used here.
Why Use This Tool
- Instantly converts an abstract percentage into a concrete, human-readable duration across four common periods.
- One-click presets for the industry-standard SLA tiers (99% through 99.999%).
- Uses the standard average month/year lengths that most SLA documentation is actually built on.
- No sign-up, entirely client-side — nothing you enter is sent anywhere.