SLA Uptime Calculator

What Do the Nines Mean?

When hosting providers and SLAs talk about “99.9% uptime,” they are describing a specific amount of allowed downtime. Each additional nine dramatically reduces that allowance — and dramatically increases the cost and complexity of achieving it.

Three nines (99.9%) is the most common SLA target for small business hosting and web applications. It allows about 8 hours and 46 minutes of downtime per year. For most SMBs, this is a reasonable target that balances cost with reliability.

Four nines (99.99%) tightens the budget to under an hour per year. Achieving this typically requires redundant infrastructure, automated failover, and professional operations. It is common for SaaS products and e-commerce platforms where downtime directly costs revenue.

Five nines (99.999%) allows only about 5 minutes of downtime per year. This is the territory of banks, hospitals, and mission-critical systems. The infrastructure, monitoring, and on-call engineering required to maintain five nines is roughly ten times the cost of four nines.

Why Fast Recovery Matters More Than Chasing Nines

For most small businesses, improving your Mean Time to Recovery (MTTR) delivers more value than trying to achieve a higher nines level. A business with 99.9% uptime and a 10-minute recovery time is in better shape than one that promises 99.99% but takes 4 hours to respond when something breaks.

The key is detection speed. If you find out about downtime within minutes instead of hours, your effective recovery time drops dramatically. That is where uptime monitoring earns its value — it turns a potential 4-hour outage into a 15-minute blip.