The Myth of Five Nines: Why You Probably Don't Need 99.999% Availability

“Five Nines.” It is the holy grail of SRE. 99.999% Availability. It allows for only 5.26 minutes of downtime per year.

New Year’s Resolutions often involve “Improving Uptime.” But before you set “Five Nines” as your goal for 2026, let’s look at the math and the money.

The Cost Curve of Reliability

Reliability does not scale linearly. It scales exponentially.

99% (Two Nines)

• Downtime: 3.65 days/year.
• Reqs: Single server, daily backups.
• Cost: $

99.9% (Three Nines)

• Downtime: 8.76 hours/year.
• Reqs: Load balancer, 2 servers, automated DB failover.
• Cost: $$ (2x cost).

99.99% (Four Nines)

• Downtime: 52 minutes/year.
• Reqs: Multi-AZ (Availability Zone), redundant load balancers, canary deployments.
• Cost: $$$$ (10x cost).

99.999% (Five Nines)

• Downtime: 5 minutes/year.
• Reqs: Multi-Region Active-Active (Deploy in US+EU), automatic DNS failover, zero-downtime database migrations.
• Cost: $$$$$$$ (50x cost).

The “User” Bottleneck

Even if your server is up 99.999% of the time, your user’s ISP (Comcast/Verizon) is only up ~99.9% of the time. The Wi-Fi in the coffee shop is only up 99% of the time.

Spending millions to be more reliable than your user’s internet connection is a waste of money.

Setting a Realistic Goal for 2026

Don’t chase a vanity number.

1. Startups: Aim for 99.5%. Speed of delivery matters more than perfection.
2. SaaS: Aim for 99.9%. Good enough for most B2B.
3. Critical Infra (Hospitals/Energy): Aim for 99.99%+.

Resolution: “I will prioritize Observability over theoretical Availability.” Knowing why you are down is more important than never being down.