Uptime / Downtime Calculator
Infrastructure Editor
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Who it's for
- Site owners comparing SLAs
- E-commerce operators
- Agencies evaluating host reliability
Hosting providers advertise uptime as a percentage — 99.9%, 99.95%, 99.99% — and it’s easy to glance at those numbers and assume they’re all roughly equivalent. They aren’t. This uptime calculator page converts the commonly advertised tiers into real downtime, so the decimal places stop being abstract. They become a comparable, decision-useful number.
The Uptime Calculator Formula
Downtime per month = (1 − uptime%) × total minutes in a month (43,200) Downtime per year = (1 − uptime%) × total minutes in a year (525,600)
Downtime by Uptime Percentage Tier
| Uptime % | Downtime per month | Downtime per year |
|---|---|---|
| 99.0% | ~7.3 hours | ~3.65 days |
| 99.5% | ~3.6 hours | ~1.83 days |
| 99.9% | ~43 minutes | ~8.7 hours |
| 99.95% | ~21 minutes | ~4.4 hours |
| 99.99% | ~4.3 minutes | ~52 minutes |
| 99.999% | ~26 seconds | ~5.3 minutes |
The jump from 99.9% to 99.99% looks small on paper — one extra 9 — but it represents roughly a tenfold reduction in downtime. That difference matters enormously for e-commerce and high-traffic sites, where even a handful of minutes offline during peak hours has a direct revenue cost. It matters far less for a low-traffic personal blog, where an extra 30 minutes of annual downtime is unlikely to be noticed.
How to Use the Uptime Calculator Table
Take the uptime percentage a host advertises and find it in the table above. Check the actual SLA document, not just the marketing page, since the two sometimes differ. Compare that downtime figure against what the site can tolerate: a marketing brochure site can absorb hours of annual downtime without meaningful harm, while a checkout flow processing live transactions cannot.
Then weigh the number against reality by checking independent, third-party uptime monitoring history for that specific provider. A written SLA and a provider’s actual track record are not always the same thing — see uptime & SLA in web hosting for how to evaluate the gap between the two.
Why Uptime Percentage Matters More for Some Sites Than Others
High-traffic sites and stores running on ecommerce hosting should treat anything below 99.95% as a serious constraint. Downtime during a traffic spike or a sales event is exactly when it’s most costly. A personal portfolio or low-traffic blog can reasonably tolerate a standard 99.9% shared-hosting tier without much practical impact.
An interactive calculator that accepts any custom uptime percentage and outputs exact downtime figures is in development for this page. Until then, the table above covers every commonly advertised tier.
Annual Downtime in Context
Framed by the year rather than the month, the gap becomes even starker: 99.9% uptime allows roughly 8.7 hours of downtime annually, while 99.99% allows under an hour. For a business that depends on its site for revenue or lead generation year-round, that’s the difference between one bad afternoon and a full unplanned business day offline. It’s worth running this annual view whenever comparing two providers whose monthly downtime figures look deceptively close.
SLA Credits Rarely Match the Real Cost of Downtime
Even when a provider misses its stated SLA, the compensation is typically a small percentage credit toward future billing. It’s rarely a cash refund, and rarely proportional to any revenue actually lost during the outage. Treat the downtime figures above as a reliability signal to compare providers by, not as a guarantee that any shortfall will be meaningfully compensated.
For the underlying concept, see what uptime is; for how uptime and SLA terms are actually negotiated and evaluated, see hosting uptime & SLA.