Acceptable downtime is usually expressed as an uptime percentage (an SLA target), and even "five nines" isn’t zero:
- 99% uptime ≈ 3.65 days of downtime per year
- 99.9% (“three nines”) ≈ 8.76 hours per year
- 99.95% ≈ 4.38 hours per year
- 99.99% (“four nines”) ≈ 52.6 minutes per year
What target should you pick?
Most small-to-mid business sites reasonably target 99.9%; e-commerce and anything processing payments in real time should push toward 99.95%–99.99%, since each minute of downtime has a direct revenue cost.
Reducing downtime
- Monitor from multiple locations to catch issues fast
- Set up a status page so support tickets don’t spike during an incident
- Have a documented rollback plan for bad deploys, the single most common cause of outages
- Keep server software and dependencies patched — unpatched software is a common indirect cause of downtime via exploits or crashes
FAQ
Does downtime hurt SEO?
Yes — if a crawler repeatedly hits a down site, rankings can drop, and prolonged outages can lead to de-indexing in extreme cases.