Guide · Updated November 2026 · Data: EIA Form 861 2025 and EIA-861M

SAIDI, SAIFI and CAIDI Explained

Every year, about 900 U.S. electric utilities report how often the lights went out and how long they stayed out, using three standardized measures. You will find them on utility profiles across this site and in our reliability rankings.

The three measures

• SAIDI (System Average Interruption Duration Index): the average total minutes of outage each customer experienced in a year. It is the headline number - the average customer's year contained this many minutes in the dark.
• SAIFI (System Average Interruption Frequency Index): the average number of sustained outages each customer experienced. A SAIFI of 1.2 means the typical customer lost power just over once.
• CAIDI (Customer Average Interruption Duration Index): SAIDI divided by SAIFI - when an outage happens, how many minutes it takes on average to get the lights back on.

What counts as good?

U.S. medians hover around 300-350 SAIDI minutes including major event days, and roughly 150-200 minutes excluding them - the two flavors are reported separately because one hurricane can triple a utility's annual figure. The best-performing utilities on the most reliable list post SAIDI under 60 minutes, thanks to underground lines, mild weather or small, dense service territories. Treat any single year cautiously: storm exposure luck dominates. A utility whose territory took a hurricane landfall will look terrible that year regardless of how well it is run.

Why comparisons are approximate

Utilities report under either the IEEE standard or their own state standard, they draw the line for "major event days" by formula, and some exclude momentary interruptions (under five minutes) that others count. Form 861 records the figures as filed, which is what this site republishes - our methodology notes the standard each utility used where it is known. The rankings apply a 10,000-customer minimum so a tiny system with one lucky year does not top the list.

Look up your utility

Search the directory for your utility; if it reports reliability data, its profile shows SAIDI, SAIFI and CAIDI next to its rates. Comparing your utility against neighbors in the same state - same weather, same storms - is the fairest quick test of whether its reliability is genuinely better or worse.

Keep exploring

Electricity rates by state · Utility rankings · Utility directory · All guides