Website Downtime Cost & Revenue Risk Calculator
Enter your host’s uptime guarantee to see exactly how many hours of downtime you’re already agreeing to. Add your revenue and traffic to see what each of those hours actually costs you.
Every hosting plan advertises an uptime guarantee — 99.9%, 99.99%, “enterprise-grade reliability.” What almost none of them tell you is what that percentage actually translates to in hours per year, or what those hours are worth to your specific business. Enter your numbers below and this calculator converts your host’s SLA into real allowed downtime and a dollar figure — the number a “cheap hosting” comparison rarely shows you.
Enter your business numbers and your host’s uptime guarantee. We’ll show you what it’s actually costing — or could cost — you.
If you’re writing about hosting SLAs or uptime guarantees, here’s a ready-to-paste link to this calculator.
How this calculator works
An uptime guarantee is a percentage of the year your host promises your site will be reachable. Flip that percentage around and it becomes a number of allowed hours of downtime per year — a number hosting marketing pages never lead with. This calculator does that conversion, then multiplies the allowed downtime by your actual revenue per hour to show what that guarantee is worth in dollars, specifically to your business.
Each additional “nine” in an uptime guarantee cuts allowed downtime by roughly 10x. Moving from 99% to 99.9% takes you from 3.65 days of allowed downtime a year down to under 9 hours. Moving from 99.9% to 99.99% takes you from 9 hours down to under an hour. The jump from three nines to four nines matters far more than most pricing pages suggest.
This calculator assumes an average hour of revenue, but real outages are not evenly distributed. A checkout failure during a product launch or a Black Friday sale costs far more than the same outage at 3am on a Tuesday — and many hosts don’t count “scheduled maintenance” against their SLA at all, even though your customers still can’t buy anything during it.
When a host misses its own SLA, the standard remedy is a service credit — typically 5% to 30% of that month’s hosting bill, not compensation for lost revenue. On a $20/month plan, even a generous 30% credit is $6. If the outage cost your business hundreds or thousands in lost sales, the “guarantee” did not actually protect you financially.
Reading your results
Here’s what the key numbers above mean.
This is the maximum downtime your host’s SLA permits before they’re considered to have broken their promise. It says nothing about how much downtime you will actually experience — only the ceiling the guarantee sets.
Your average monthly revenue divided across the hours in a month. This is the number worth remembering on its own — it’s what one hour of outage costs you, regardless of whose fault it is or what the SLA says.
Your hourly revenue rate multiplied by the allowed downtime. This is the dollar amount baked into your current SLA even if your host hits their target exactly — before accounting for any outages beyond what they’ve promised.
If you entered a real measured uptime figure, this shows the extra downtime beyond what your SLA allows, and what that gap has actually cost you — the number most relevant if you’re deciding whether to switch hosts.
Frequently asked questions
It depends entirely on your business — there is no universal figure, despite what some headlines claim. The calculator above gives you your specific number by dividing your average monthly revenue across the hours in a month. A site generating $15,000/month averages roughly $20/hour; a site generating $500,000/month averages roughly $685/hour. Multiply that by however many hours you expect to be down, planned or unplanned, to get a realistic estimate for your business.
They describe the maximum downtime a host commits to over a year before you’re entitled to a service credit. 99.9% allows about 8 hours 46 minutes of downtime per year; 99.99% allows about 53 minutes; 99% allows about 3 days and 15.5 hours. These are ceilings the host has promised not to exceed — not a prediction of how much downtime you’ll actually see, which can be better or worse.
Almost always in the form of a service credit against a future invoice, not cash, and calculated as a percentage of your hosting fee — not your lost revenue. Read your host’s SLA document specifically for the words “sole remedy,” which is standard language stating the credit is the only compensation you’re entitled to, regardless of how much the outage actually cost your business.
For most small business and content sites, yes — 8 hours 46 minutes of allowed downtime a year is a reasonable baseline, especially if outages tend to be short and infrequent rather than one long incident. For a site where even a short outage costs real revenue (ecommerce checkout, SaaS login, a high-traffic launch day), the jump to 99.95% or 99.99% removes a meaningful amount of risk for a comparatively small cost increase — use the calculator above with your own revenue figure to see whether that trade-off is worth it for you specifically.
Free tools like UptimeRobot, Pingdom, or StatusCake check your site every few minutes from outside your host’s network and log an independent uptime percentage over time — usually free for a single site. Run one for at least a month before trusting the number, since a single bad week can skew a short measurement period.
Most hosting SLAs explicitly exclude scheduled maintenance windows from their uptime calculation, as long as the host gives advance notice. That means a host can be technically “meeting” a 99.99% SLA while your site is still unreachable during announced maintenance — your customers experience downtime either way, but it may not count against the guarantee or entitle you to a credit.
Independent uptime monitoring with instant alerts, a documented incident response plan, offsite backups tested for fast restoration, and a status page for customers all reduce the practical impact of an outage even on the same hosting plan. If your calculated revenue at risk is high, though, the underlying infrastructure — load balancing, failover, or multi-region redundancy — is what actually prevents the outage rather than just softening its impact.
An uptime guarantee is a promise on paper.
The percentage on a hosting pricing page tells you what a company is willing to commit to, backed by a credit worth a fraction of what an outage might actually cost you. It does not tell you how reliable that host has actually been, and it says nothing about what an hour of downtime is worth to your specific business.
Know your real number before an outage puts it in front of your customers instead.